Mutated rep encoding sequences for use in AAV production

ABSTRACT

Nucleic acids encoding Parvoviral Rep proteins with a mutated nuclear localization signal (NLS) are provided. Also provided is a nucleic acid comprising a nucleotide sequence encoding a Parvoviral Rep protein with a mutated zinc finger domain and a nucleic acid comprising a nucleotide sequence encoding a Parvoviral Rep protein comprising an amino acid mutation at position 43, 57, 79, 97, 120, 179, 305, 484, 493 or 571 with reference to SEQ ID NO: 2. Nucleic acid constructs and cells, such as insect cells, comprising the nucleic acids are provided as well as a method for producing a recombinant Parvoviral virion using the nucleic acids.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No. 13/583,920, filed Sep. 10, 2012, filed as the National Phase of International Patent Application No. PCT/NL2014/050170, filed Mar. 11, 2011, published on Sep. 15, 2011 as WO 2011/112089 A2, which claims priority to U.S. Provisional Application No. 61/312,845, filed Mar. 11, 2010. The contents of which are herein incorporated by reference in their entirety.

The instant application contains a Sequence Listing which has been submitted in ASCII format via EFS-WEB and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Apr. 10, 2017, is named Sequence.txt and is 144 KB.

FIELD OF THE INVENTION

The present invention relates to nucleic acids which encode mutant Parvoviral Rep sequences. The invention also relates to nucleic acid constructs and cells, such as insect cells, which comprise the nucleic acids. The invention further relates to a method for producing a recombinant Parvoviral virion using the nucleic acids.

BACKGROUND OF THE INVENTION

Adeno-associated virus (AAV) is considered one of the most promising viral vectors for human gene therapy. AAV has the ability to efficiently infect dividing as well as non-dividing human cells, the AAV viral genome integrates into a single chromosomal site in the host cell's genome, and most importantly, even though AAV is present in many humans, it has never been associated with any disease. In view of these advantages, recombinant adeno-associated virus (rAAV) is being evaluated in gene therapy clinical trials, inter alia, for hemophilia B, malignant melanoma, cystic fibrosis.

Host cells that sustain AAV replication in vitro are all derived from mammalian cell types. Therefore, rAAV for use in gene therapy has traditionally been produced on mammalian cell lines such as e.g. 293 cells, COS cells, HeLa cells, KB cells, and other mammalian cell lines. However, in most mammalian cell culture systems, the number of AAV particles generated per cell is of the order of 10⁴ particles (reviewed in Clark, 2002, Kidney Int. 61 (Suppl. 1): 9-15). For a clinical study, more than 10¹⁵ particles of rAAV may be required. To produce this number of rAAV particles, transfection and culture with approximately 10¹¹ cultured human 293 cells, the equivalent of 5,000 175-cm² flasks of cells, would be required, which means transfecting up to 10¹¹ 293 cells. Therefore, large scale production of rAAV using mammalian cell culture systems to obtain material for clinical trials has already proven to be problematic, production at commercial scale may not even be feasible. Furthermore there is always the risk, that a vector for clinical use that is produced in a mammalian cell culture will be contaminated with undesirable, perhaps pathogenic, material present in the mammalian host cell.

To overcome these problems of mammalian productions systems, recently, an AAV production system has been developed using insect cells (Urabe et al., 2002, Hum. Gene Ther. 13: 1935-1943; US 20030148506 and US 20040197895). This baculovirus expression vector system (BEVS) is based on infection of insect cells with baculoviruses containing a gene to be expressed flanked by AAV ITRs, a baculovirus expressing the AAV rep gene and a baculovirus encoding the AAV cap gene leading to production of infectious rAAV particles. If desired, the AAV rep and cap genes may be present on the same baculovirus

However, despite various improvements to the basic system, it is still problematic that more capsids appear to be empty rather than being loaded with the therapeutic gene of interest. There is thus still a need to overcome this limitation so as to improve large scale (commercial) production of AAV vectors in insect cells. Thus it is an object of the present invention to provide for means and methods that allow for stable and high yield (large scale) production of AAV vectors in insect cells.

BRIEF DESCRIPTION OF THE INVENTION

The invention relates to mutant Parvoviral Rep polypeptides/proteins, such as AAV Rep polypeptides/proteins, and to nucleic acids which encode those mutant polypeptides. The nucleic acids may be used in the preparation of Parvoviruses, in particular in the preparation of recombinant adeno-associated viruses (AAV). A mutant/mutated polypeptide/protein is one which is different from its corresponding wild type sequence. A mutant/mutated polypeptide/protein may typically be one which does not exist in nature.

The mutant Parvoviral Rep polypeptides typically possess one or more improved properties as compared with their corresponding wild type Rep polypeptide. Thus they may be used to prepare higher virus titres, for example, than a corresponding wild type Rep polypeptide. In addition, or alternatively, they may be able to allow the production of better quality viral particles or sustain more stable production of virus.

According to the invention, there is thus provided a nucleic acid comprising a nucleotide sequence encoding a Parvoviral Rep protein, wherein a nuclear localization signal (NLS) in said Parvoviral Rep protein is mutated as compared with a corresponding wild type sequence.

The invention also provides a nucleic acid comprising a nucleotide sequence encoding a Parvoviral Rep protein, wherein the zinc finger domain in said Parvoviral Rep protein is mutated as compared with a corresponding wild type sequence.

Further, the invention provides a nucleic acid according to any one of the preceding claims which encodes a Parvoviral Rep protein, wherein the codon encoding the amino acid at position 493 or 571 is substituted with a stop codon, said amino acid position being defined with reference to SEQ ID NO: 1.

In addition, the invention provides:

-   -   a nucleic acid comprising a nucleotide sequence encoding a         Parvoviral Rep protein, wherein an amino acid at position 43,         57, 79, 97, 120, 179, 305, 484, 493 or 571 of the said         Parvoviral Rep protein is mutated in comparison to a         corresponding wild type sequence, said amino acid position being         defined with reference to SEQ ID NO: 2;     -   a nucleic acid comprising the nucleotide sequence set out in any         one of SEQ ID NOs: 5, 7, 9, 11, 13, 15, 17, 19 or 21;     -   a nucleic acid comprising a nucleotide sequence encoding the Rep         protein as set out in any one of SEQ ID NOs: 6, 8, 10, 12, 14,         16, 18, 20 or 22;     -   a nucleic acid comprising two or more nucleotide sequences which         encode a Parvoviral Rep protein, one or more of which is a         nucleic acid as described herein;     -   a Parvoviral Rep protein as defined above or as encoded by a         nucleic acid as defined above;     -   a nucleic acid construct comprising a nucleic acid as described         herein, wherein the said nucleic acid is operably linked to an         expression control sequence for expression in an insect cell;     -   an insect cell comprising a nucleic acid or a nucleic acid         construct as described herein; and     -   a method for the production of a recombinant Parvoviral virion         in an insect cell, the virion comprising a nucleic acid of the         invention operably linked to an expression control sequence for         expression in an insect cell, which method comprises:     -   (i) culturing an insect cell as defined above,         -   wherein the insect cell further comprises: a nucleic acid             comprising at least one Parvoviral inverted terminal repeat             (ITR) nucleotide sequence; and a nucleic acid sequence             comprising a nucleotide sequence encoding Parvoviral capsid             protein coding sequence operably linked to expression             control sequences for expression in an insect cell,     -   under conditions such that a recombinant parvoviral virion is         produced; and,     -   (ii) recovering the recombinant parvoviral virion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of pVD142(lot #2).

FIG. 2 shows a schematic representation of pVD156

FIG. 3 shows a schematic representation of pVD143.

FIGS. 4A, 4B, and 4C show the restriction analysis of the two different pVD142-Rep-EP libraries A) PstI-EagI restriction fragments of pVD142. B) PstI-EagI restriction fragments of pVD143.C) An agarose gel showing restriction fragments of pVD142 (1), pVD143 (2), pVD142-Rep-EP1 (3) and pVD142-Rep-EP3 (4) digested with PstI-EagI. M, Smartladder (Eurogentec). The lower panel is overexposed to detect the 175 bp fragment.

FIG. 5 shows the quality control of Bac.Rep-EP libraries. Baculoviral DNA was isolated from p0 and p1 baculovirus stocks and used in an insert control PCR using primerset #349/350. As shown for all baculovirus stocks this resulted predominantly in a ˜1.9 kbp fragment. Four different plasmids were used as positive controls (lane 2-4). M, smartladder (Eurogentec).

FIGS. 6A, 6B, and 6C show the amplified Rep-EP3 sequences selected after the first selection round, the introduction of new mutations and restriction analysis of the two new libraries. A) Schematic overview of the viral DNA isolated after the first selection round. The primer binding sites that flank the selected Rep-EP3 sequences are indicated by pr321-pr324. B) C) An agarose gel showing the amplified PCR products when using the AMT primer set #321/#322 and different amounts of viral DNA input isolated after the first selection round. The 1869 bp fragments were isolated from gel and 10 ng was used as a template in the EP-PCR to introduce new mutations. D) Restriction analysis of the two new libraries pVD142-select-EP3 and pVD142-EP-EP3 using PstI-EagI. M, smartladder (Eurogentec).

FIG. 7 shows the quality control of the Rep-EP libraries second selection round used in the second selection round. Baculoviral DNA isolated from p1 baculovirus stocks was used in an insert control PCR using primerset #349/350. Except for Bac.VD142, all baculovirus stocks revealed the presence of the correct 1.9 kbp fragment. Plasmids pVD142 and pVD143 were used as positive controls (lane 2-3).

FIG. 8 shows the amplified selected Rep-EP-EP3 sequences after the second selection round when using the AMT primer set #323/#324 and different amounts of viral DNA template. The 1915 bp fragment obtained with the PCR in lane 5 was isolated from gel and cloned to pDONR221, resulting in the pDONR221-selectEP-EP3 library. Plasmids pVD142 and pVD143 are used as a negative control and positive control in the two different PCR reactions. M, smartladder (Eurogentec).

FIGS. 9A and 9B show the virus titers of rAAV5 productions with Bac.Rep-select-EP-EP3 clones 1-20 and the control productions with Bac.VD142 and Bac.VD143. A) Virus titers of the rAAV5 productions using the different clones were determined in crude lysates with the Q-PCR method. Clones 4, 6, 7, 9 and 15 generated virus titers that were comparable to background level (Bac.VD142). Clones 1 and 3 gave comparable titers as the positive control Bac.VD143 (FIG. 9A, black bar), while clones 8, 12 and 16-18 generated higher virus titers. Productions with all other clones resulted in lower virus titers as the Bac.VD143, but were above background level. B) Virus titers of the rAAV5 productions using plaque purified clones were determined in crude lysates using the Q-PCR method. Productions with clones 12, 13 and 16-20 gave virus titers that were in the range of 1-2×10¹¹ gc/ml, while the positive control production with Bac.VD143 (black bar) resulted in a titer of 4×10¹⁰ gc/ml. The negative control production with Bac.VD142 generated a value of 8.4×10⁷ gc/ml.

FIGS. 10A and 10B show the Rep protein expression from Rep baculovirus constructs comprising the YF mutations. A) Schematic overview of the different Rep baculovirus constructs comprising the YF mutations and the control constructs Bac.VD88, −228 and −210. Numbers indicate the amino acid numbering according to Rep78. Amino acid changes in the Rep proteins compared to Bac.VD88 are shown in capital letters and the silent mutations (only present in the DNA) are indicated by X. At the upper part a schematic overview of the Rep78 and Rep52 replication proteins is shown which are expressed by Bac.VD88. Functional domains present in the Rep proteins are indicated at the top (Chiorini, J. A., F. Kim, L. Yang, and R. M. Kotin. (1999) J. Virol. 73:1309-1319). Trs, terminal resolution site; NLS, nuclear localization signal; Zn finger, Zinc finger; regions necessary for multimerization are depicted by striped boxes. B) A representative western blot analysis showing the Rep protein expression from the different Rep baculovirus constructs during a rAAV5 production. Protein lysates were harvested 24 h p.i. The shortened Rep forms expressed from Bac.VD210 and Bac.VD215-218 are indicated with arrows and named Reppy78 and Reppy52.

FIGS. 11A and 11B show the Rep protein expression from Rep baculovirus constructs comprising the GPR mutations. A) Schematic overview of the different Rep baculovirus constructs comprising the GPR mutations and the control constructs Bac.VD88, −228 and −210. Numbers indicate the amino acid numbering according to Rep78. Amino acid changes in the Rep proteins compared to Bac.VD88 are shown in capital letters and the silent mutations (only present in the DNA) are indicated by X. At the upper part a schematic overview of the Rep78 and Rep52 replication proteins is shown which are expressed by Bac.VD88. Functional domains present in the Rep proteins are indicated at the top (Chiorini, J. A., F. Kim, L. Yang, and R. M. Kotin. (1999) J. Virol. 73:1309-1319). Trs, terminal resolution site; NLS, nuclear localization signal; Zn finger, Zinc finger; regions necessary for multimerization are depicted by striped boxes. B) A representative western blot analysis showing the Rep protein expression from the different Rep baculovirus constructs during a rAAV5 production. Protein lysates were harvested 24 h p.i. The shortened Rep forms expressed from Bac.VD210, Bac.VD214 and Bac.VD220 are indicated with arrows and named Reppy78 and Reppy52.

FIGS. 12A and 12B show the CMV-SEAP transgene replication during rAAV5 production using the different Rep baculovirus constructs. Representative agarose gels showing the LMW-DNA isolated from rAAV5 productions using the Rep baculovirus constructs comprising the YF (A) or GPR (B) mutations and the control constructs. LMW-DNA was isolated from cell pellets that were harvested 1, 2 and 3 days p.i. The monomeric and dimeric replicative forms of the transgene are indicated with RFm and RFd, respectively. Higher order forms are only indicated with arrows.

FIG. 13 shows the virus titers of rAAV5 productions performed with the different Rep baculovirus constructs. Virus titers were determined in clarified crude lysates using the CMV Q-PCR method. Productions with Bac.VD216 and Bac.VD217 significantly improved the virus titers, while Bac.VD228 reduced the virus titer. Results are indicated as mean±S.E.M. (n=3) and calculated as fold to Bac.VD88, which was set as 1 in all three experiments.

FIG. 14 shows the total/full particle ratio of rAAV5 particles produced with indicated Rep baculovirus constructs. Ratios were determined using SyproRuby staining of total proteins and Q-PCR analysis. Productions with Bac.VD216 and Bac.VD217 significantly improved the total/full ratio. Results are represented as mean±S.E.M and n=6.

FIGS. 15A, 15B, 15C, and 15D show the amount of residual baculovirus DNA in rAAV5 batch purified samples as ratio from the transgene. A) Schematic overview of the transgene part in baculovirus Bac.VD179 which is flanked by ORF603 and ORF1629 and residual DNA primers that target the left ORF (pr406/407) and the right ORF (pr180/181) are shown in the picture. Primer set pr59/60 targets the CMV promoter and is used to determine the ratio between transgene and residual DNA present in the batches. The HR3 primer set is not shown. B) The amount of residual left ORF DNA determined with pr406/407 is shown as the CMV/left ORF ratio. Productions with Bac.VD210, −217 and −220 resulted in a 3-5 fold reduction of residual DNA in the rAAV5 batches as compared to Bac.VD88. C) The amount of residual right ORF DNA determined with pr180/181 is shown as the CMV/right ORF ratio. All Rep mutant constructs reduce the amount of right ORF residual DNA with a 5-13 fold as compared to Bac.VD88. D) The amount of residual HR3 DNA determined with pr340/341 is shown as the CMV/HR3 ORF ratio. All Rep mutant constructs reduce the amount of HR3 residual DNA with a 25-52 fold. All results are represented as mean±S.E.M and n=6. Statistical analysis involved the ANOVA single factor test and was compared to Bac.VD88. * p<0.05.

FIGS. 16A, 16B, 16C, 16D, 16E, 16F, and 16G show a sequence comparison of VD88 (SEQ ID NO:3), VD210 (SEQ ID NO:5), VD211 (SEQ ID NO:7), VD212 (SEQ ID NO:9), VD214 (SEQ ID NO:11), VD215 (SEQ ID NO:13), VD216 VD217 (SEQ ID NO:17), VD218 (SEQ ID NO:19) and VD220 (SEQ ID NO:21).

BRIEF DESCRIPTION OF THE SEQUENCE LISTING

SEQ ID NO: 1 sets out the full length nucleotide sequence of Rep78 from AAV2.

SEQ ID NO: 2 sets out the full length amino acid sequence of Rep78 from AAV2.

SEQ ID NO: 3 sets out the nucleotide sequence of VD88.

SEQ ID NO: 4 sets out the amino acid sequence of VD88.

SEQ ID NO: 5 sets out the nucleotide sequence of VD210.

SEQ ID NO: 6 sets out the amino acid sequence of VD210.

SEQ ID NO: 7 sets out the nucleotide sequence of VD211.

SEQ ID NO: 8 sets out the amino acid sequence of VD211.

SEQ ID NO: 9 sets out the nucleotide sequence of VD212.

SEQ ID NO: 10 sets out the amino acid sequence of VD212.

SEQ ID NO: 11 sets out the nucleotide sequence of VD214.

SEQ ID NO: 12 sets out the amino acid sequence of VD214.

SEQ ID NO: 13 sets out the nucleotide sequence of VD215.

SEQ ID NO: 14 sets out the amino acid sequence of VD215.

SEQ ID NO: 15 sets out the nucleotide sequence of VD216.

SEQ ID NO: 16 sets out the amino acid sequence of VD216.

SEQ ID NO: 17 sets out the nucleotide sequence of VD217.

SEQ ID NO: 18 sets out the amino acid sequence of VD217.

SEQ ID NO: 19 sets out the nucleotide sequence of VD218.

SEQ ID NO: 20 sets out the amino acid sequence of VD218.

SEQ ID NO: 21 sets out the nucleotide sequence of VD220.

SEQ ID NO: 22 sets out the amino acid sequence of VD220.

DETAILED DESCRIPTION OF THE INVENTION

The present invention concerns animal parvoviruses, in particular dependoviruses such as infectious human or simian AAV, and the components thereof (e.g., an animal parvovirus genome). In particular, the invention relates to nucleic acids which encode mutant Rep polypeptides/proteins.

Parvoviruses may be used as vectors for introduction and/or expression of nucleic acids in mammalian cells. Thus, the invention concerns improvements to productivity and/or quality of such parvoviral vectors when produced in insect cells.

Viruses of the Parvoviridae family are small DNA animal viruses. The family Parvoviridae may be divided between two subfamilies: the Parvovirinae, which infect vertebrates, and the Densovirinae, which infect insects. Members of the subfamily Parvovirinae are herein referred to as the parvoviruses and include the genus Dependovirus. As may be deduced from the name of their genus, members of the Dependovirus are unique in that they usually require coinfection with a helper virus such as adenovirus or herpes virus for productive infection in cell culture.

The genus Dependovirus includes AAV, which normally infects humans (e.g., serotypes 1, 2, 3A, 3B, 4, 5, and 6) or primates (e.g., serotypes 1 and 4), and related viruses that infect other warm-blooded animals (e.g., bovine, canine, equine, and ovine adeno-associated viruses). Further information on parvoviruses and other members of the Parvoviridae is described in Kenneth I. Berns, “Parvoviridae: The Viruses and Their Replication,” Chapter 69 in Fields Virology (3d Ed. 1996). For convenience the present invention is further exemplified and described herein largely by reference to AAV. It is, however, understood that the invention is not limited to AAV but may equally be applied to other parvoviruses.

The genomic organization of all known AAV serotypes is very similar. The genome of AAV is a linear, single-stranded DNA molecule that is less than about 5,000 nucleotides (nt) in length. Inverted terminal repeats (ITRs) flank the unique coding nucleotide sequences for the non-structural replication (Rep) proteins and the structural (VP) proteins. The VP proteins (VP1, −2 and −3) form the capsid. The terminal 145 nt are self-complementary and are organized so that an energetically stable intramolecular duplex forming a T-shaped hairpin may be formed. These hairpin structures function as an origin for viral DNA replication, serving as primers for the cellular DNA polymerase complex. Following wtAAV infection in mammalian cells the Rep genes (i.e. Rep78 and Rep52) are expressed from the P5 promoter and the P19 promotor, respectively and both Rep proteins have a function in the replication of the viral genome. A splicing event in the Rep ORF results in the expression of actually four Rep proteins (i.e. Rep78, Rep68, Rep52 and Rep40). However, it has been shown that the unspliced mRNA, encoding Rep78 and Rep52 proteins, in mammalian cells are sufficient for AAV vector production. Also in insect cells the Rep78 and Rep52 proteins suffice for AAV vector production.

The invention relates to a nucleic acid comprising a nucleotide sequence encoding a mutant Parvoviral Rep protein. That is to say, a nucleic acid of the invention encodes a non-wild type Parvoviral Rep protein. Typically, a nucleic acid of the invention encodes a non-wild type AAV Rep protein.

As set out above, the present invention provides a nucleic acid encoding the variant polypeptides of the invention. The invention also relates to an isolated polynucleotide encoding at least one functional domain of a polypeptide variant of the invention. Typically, such a domain will comprise one or more of the mutations described herein.

In one embodiment of the invention, the nucleic acid sequence according to the invention encodes a polypeptide, wherein the polypeptide is a variant comprising an amino acid sequence that has a mutation, for example one or more truncation(s), and/or at least one substitution, deletion and/or insertion of an amino acid as compared to a corresponding wild type Rep protein. Typically, mutations in the invention are substitutions, i.e. one amino acid is replaced with an amino acid that does not typically appear at the relevant position in the corresponding wild type sequence. Such a polypeptide will, however, typically comprise one or more of the mutations, in particular substitutions, described herein.

As used herein, the terms “gene” and “recombinant gene” refer to nucleic acid molecules which include an open reading frame encoding a variant as described herein. A gene may include coding sequences, non-coding sequences, introns and regulatory sequences. That is to say, a “gene”, as used herein, may refer to an isolated nucleic acid molecule as defined herein. Accordingly, the term “gene”, in the context of the present application, does not refer only to naturally-occurring sequences.

A nucleic acid molecule of the present invention can be generated using standard molecular biology techniques well known to those skilled in the art taken in combination with the sequence information provided herein. For example, using standard synthetic techniques, the required nucleic acid molecule may be synthesized de novo. Such a synthetic process will typically be an automated process.

Alternatively, a nucleic acid molecule of the invention may be generated by use of site-directed mutagenesis of an existing nucleic acid molecule, for example a wild-type nucleic acid molecule. Site-directed mutagenesis may be carried out using a number of techniques well know to those skilled in the art.

In one such method, mentioned here merely by way of example, PCR is carried out on a plasmid template using oligonucleotide “primers” encoding the desired substitution. As the primers are the ends of newly-synthesized strands, should there be a mis-match during the first cycle in binding the template DNA strand, after that first round, the primer-based strand (containing the mutation) would be at equal concentration to the original template. After successive cycles, it would exponentially grow, and after 25, would outnumber the original, unmutated strand in the region of 8 million: 1, resulting in a nearly homogeneous solution of mutated amplified fragments. The template DNA may then be eliminated by enzymatic digestion with, for example using a restriction enzyme which cleaves only methylated DNA, such as Dpn1. The template, which is derived from an alkaline lysis plasmid preparation and therefore is methylated, is destroyed in this step, but the mutated plasmid is preserved because it was generated in vitro and is unmethylated as a result.

In such a method more than one mutation (encoding a substitution as described herein) may be introduced into a nucleic acid molecule in a single PCR reaction, for example by using one or more oligonucleotides, each comprising one or more mis-matches. Alternatively, more than one mutation may be introduced into a nucleic acid molecule by carrying out more than one PCR reaction, each reaction introducing one or more mutations, so that altered nucleic acids are introduced into the nucleic acid in a sequential, iterative fashion.

A nucleic acid of the invention can be generated using cDNA, mRNA or alternatively, genomic DNA, as a template and appropriate mis-matched oligonucleotide primers according to the site-directed mutagenesis technique described above. A nucleic acid molecule derived in this way can be cloned into an appropriate vector and characterized by DNA sequence analysis.

A nucleic acid sequence of the invention may comprise one or more deletions, i.e. gaps, in comparison to the parent asparaginase. Such deletions/gaps may also be generated using site-directed mutagenesis using appropriate oligonucleotides. Techniques for generating such deletions are well known to those skilled in the art.

Furthermore, oligonucleotides corresponding to or hybridizable to nucleotide sequences according to the invention can be prepared by standard synthetic techniques, e.g., using an automated DNA synthesizer.

Also, complementary nucleic acid molecules are included in the present invention. A nucleic acid molecule which is complementary to another nucleotide sequence is one which is sufficiently complementary to the other nucleotide sequence such that it can hybridize to the other nucleotide sequence thereby forming a stable duplex.

One aspect of the invention pertains to isolated nucleic acid molecules that encode a variant of the invention, or a biologically active fragment or domain thereof, as well as nucleic acid molecules sufficient for use as hybridization probes to identify nucleic acid molecules encoding a polypeptide of the invention and fragments of such nucleic acid molecules suitable for use as PCR primers for the amplification or mutation of nucleic acid molecules, such as for the preparation of nucleic acid molecules of the invention.

An “isolated polynucleotide” or “isolated nucleic acid” is a DNA or RNA that is not immediately contiguous with both of the coding sequences with which it is immediately contiguous (one on the 5′ end and one on the 3′ end) in the naturally occurring genome of the organism from which it is derived. Thus, in one embodiment, an isolated nucleic acid includes some or all of the 5′ non-coding (e.g., promotor) sequences that are immediately contiguous to the coding sequence. The term therefore includes, for example, a recombinant DNA that is incorporated into a vector, into an autonomously replicating plasmid or virus, or into the genomic DNA of a prokaryote or eukaryote, or which exists as a separate molecule (e.g., a cDNA or a genomic DNA fragment produced by PCR or restriction endonuclease treatment) independent of other sequences. It also includes a recombinant DNA that is part of a hybrid gene encoding an additional polypeptide that is substantially free of cellular material, viral material, or culture medium (when produced by recombinant DNA techniques), or chemical precursors or other chemicals (when chemically synthesized). Moreover, an “isolated nucleic acid fragment” may be a nucleic acid fragment that is not naturally occurring as a fragment and would not be found in the natural state.

As used herein, the terms “polynucleotide” or “nucleic acid (molecule)” are intended to include DNA molecules (e.g., cDNA or genomic DNA) and RNA molecules (e.g., mRNA) and analogs of the DNA or RNA generated using nucleotide analogs. The nucleic acid molecule can be single-stranded or double-stranded, but preferably is double-stranded DNA. The nucleic acid may be synthesized using oligonucleotide analogs or derivatives (e.g., inosine or phosphorothioate nucleotides). Such oligonucleotides can be used, for example, to prepare nucleic acids that have altered base-pairing abilities or increased resistance to nucleases.

A nucleotide sequence encoding a mutant Parvoviral Rep protein, is herein understood as a nucleotide sequence encoding a non-structural Rep protein. A nucleic acid sequence of the invention may comprise sequences encoding more than one Rep protein (at least one of which is a mutant Rep protein), in particular those that are required and sufficient for parvoviral vector production in insect cells such the Rep78, Rep52, Rep 68 or Rep 40 proteins.

The Parvovirus nucleic acid of the invention preferably is from a dependovirus, more preferably from a human or simian adeno-associated virus (AAV) and most preferably from an AAV which normally infects humans (e.g., serotypes 1, 2, 3A, 3B, 4, 5, 6, 7, 8 or 9) or primates (e.g., serotypes 1 and 4).

An example of a nucleotide sequence encoding animal parvoviruses Rep proteins is given in SEQ ID NO: 1, which depicts the wild type sequence encoding the Rep 78 and Rep 52 proteins from AAV2. The full length coding sequence encodes the Rep 78 protein. It is understood that the exact molecular weights of the Rep78 and Rep52 proteins, as well as the exact positions of the translation initiation codons may differ between different parvoviruses. However, the skilled person will know how to identify the corresponding position(s) in a nucleotide sequence from parvoviruses other than AAV2, for example by carrying out an alignment.

A nucleotide sequence encoding an animal parvovirus Rep protein may thus also be defined as a nucleotide sequence:

-   -   a) that encodes a polypeptide comprising an amino acid sequence         that has at least 50, 60, 70, 80, 88, 89, 90, 95, 97, 98, or 99%         sequence identity with the amino acid sequence of SEQ ID NO. 2;     -   b) that has at least 50, 60, 70, 80, 81, 82, 85, 90, 95, 97, 98,         or 99% sequence identity with the nucleotide sequence of         positions 11-1876 of SEQ ID NO. 1;     -   c) the complementary strand of which hybridises to a nucleic         acid molecule sequence of (a) or (b);     -   d) nucleotide sequences the sequence of which differs from the         sequence of a nucleic acid molecule of (c) due to the degeneracy         of the genetic code.

A nucleic acid of the invention may encode more than one animal Parvoviruse Rep protein and may encode the Rep proteins that are required and sufficient for parvoviral vector production in insect cells.

A nucleic acid of the invention may comprise a nucleotide sequence encoding a Parvoviral Rep protein, wherein a nuclear localization signal (NLS) in said Parvoviral Rep protein is mutated with respect to the wild type sequence.

In the wild type AAV2 Rep78 protein, there are three putative NLS sequences located at positions 484-491, 492-494 and 506-509 of SEQ ID NO: 2. One, two or all three of said sites may be mutated, in particular carry one or more substituted amino acids, in a mutant Parvoviral Rep protein encoded by a nucleic acid of the invention. These mutations typically reduce the ability of the NLS to act as an NLS.

A nucleic acid of the invention may encode a mutant Parvoviral Rep protein, wherein an NLS (or two or more NLSs) is at least partially truncated and/or deleted.

A nucleic acid of the invention may be truncated such that the encoded Rep protein is truncated in comparison to the corresponding wild type sequence such that said truncation results in mutation of an NLS (or two or more NLSs) encoded by the nucleic acid. The truncation may result in partial or complete deletion of one or more NLS sequences.

According to the invention, there is also provided a nucleic acid comprising a nucleotide sequence encoding a Parvoviral Rep protein, wherein the zinc finger domain in said Parvoviral Rep protein is mutated with respect to the corresponding wild type sequence.

Herein, reference to a corresponding wild type sequence indicates the wild type sequence from which a variant nucleic acid of the invention is derived, for example the wild type sequence of AAV2 Rep78 where the variant is a variant of that sequence.

With reference to the wild type AAV2 Rep78 protein (SEQ ID NO: 2), the zinc finger sequence is located at from about amino acid 526 to about amino acid 621.

A nucleic acid according of the invention may encode a Rep protein in which the zinc finger domain is at least partially mutated, such as carrying one or more substitutions or is truncated and/or deleted.

Accordingly, a nucleic acid of the invention may encode a Rep protein which is truncated with respect to the corresponding wild type sequence such that said truncation results in mutation of the zinc finger domain encoded by the nucleic acid.

These mutations will typically result in the zinc finger domain having a reduced ability to operate as a zinc finger domain.

The invention provides, in particular, a nucleic acid according to any one of the preceding claims which encodes a Parvoviral Rep protein, wherein the codon encoding the amino acid at position 493 or 571 is substituted with a stop codon, said amino acid position being defined with reference to SEQ ID NO: 2 (wild type Rep78 from AAV2). That is to say, the nucleic acid is truncated at one of the two positions mentioned.

A nucleic acid of the invention may comprise mutations both to the sequences encoding the zinc finger domain and to one or more sequence encoding an NLS. That is to say, these types of mutations may be combined in a single nucleic acid of the invention.

Further provided by the invention is a nucleic acid comprising a nucleotide sequence encoding a Parvoviral Rep protein, wherein an amino acid at position 43, 57, 79, 97, 120, 179, 305, 484, 493 or 571 of the said Parvoviral Rep protein is mutated with respect to the wild type sequence, said amino acid position being defined with reference to SEQ ID NO: 2. Typically, these mutations will be substitutions, i.e. the amino acid which appears at a position in the wild type is replaced with an amino acid that does not typically appear at that position.

A nucleic acid of the invention may be defined by a combination of two or more of the above-mentioned mutations.

Such a nucleic acid of the invention may encode a Rep polypeptide, wherein amino acids at positions:

-   -   79 and 120;     -   57, 97 and 179;     -   57, 97, 179 and 484;     -   43, 79 and 120;     -   79 and 120; or     -   79, 120 and 305.     -   are mutated with respect to the corresponding wild type         sequence, said amino acid positions being defined with reference         to SEQ ID NO: 2.

Any one of these combinations may further be combined with the mutations at positions 493 or 571, said amino acid positions being defined with reference to SEQ ID NO: 2.

The following two Tables set out combinations of mutations which may be used to define a nucleic acid of the invention. The positions set out in the Tables are defined with reference to the Rep78 sequence from AAV2 (SEQ ID NO: 2). Clearly, at the nucleotide sequence level, any mutation may be used which effects the amino acid mutation set out in Table 2. Table 1 gives specific, non-limiting examples of how that may be achieved.

TABLE 1 Nucleotide mutations in Rep baculovirus constructs Baculovirus Rep sequence (bp) Nucleotide mutations Bac.VD210 1476 Bac.VD211 1866 nt236(T > A) nt358(A > T) Bac.VD212 1866 nt170(A > G) nt289(A > C) nt535(T > C) nt642(G > T) Bac.VD214 1720 nt170(A > G) nt289(A > C) nt535(T > C) nt642(G > T) nt894(T > A) nt1450(T > C) Bac.VD215 1476 nt127(A > G) nt236(T > A) nt358(A > T) nt633(T > C) Bac.VD216 1476 nt127(A > G) nt236(T > A) nt358(A > T) Bac.VD217 1476 nt236(T > A) nt358(A > T) Bac.VD218 1476 nt236(T > A) nt358(A > T) nt914(A > G) Bac.VD219 1476 nt236(T > A) nt358(A > T) Bac.VD220 1476 nt170(A > G) nt289(A > C) nt535(T > C) nt642(G > T)

TABLE 2 Amino acids mutations in Rep baculovirus constructs Baculovirus Rep sequence (bp) Amino acids mutations Bac.VD210 1476 493K->stop Bac.VD211 1866 79F->Y 120I->F Bac.VD212 1866 57E->G 97T->P 179C->R Bac.VD214 1720 57E->G 97T->P 179C->R 484F->L 571C->stop Bac.VD215 1476 43M->V 79F->Y 120I->F 493K->stop Bac.VD216 1476 43M->V 79F->Y 120I->F 493K->stop Bac.VD217 1476 79F->Y 120I->F 493K->stop Bac.VD218 1476 79F->Y 120I->F 305N->S 493K->stop Bac.VD219 1476 79F->Y 120I->F 493K->stop Bac.VD220 1476 57E->G 97T->P 179C->R

A nucleic acid as described above may encode a Rep protein having at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, at least about 98% or at least about 99% or higher sequence similarity to a corresponding wild type Rep protein sequence, i.e. to the wild type sequence from which it is derived. That is to say, a nucleic acid of the invention may have additional differences from a wild type sequence other than those described above.

A nucleic acid of the invention will typically display improved properties as compared to its corresponding wild type sequence. For example, it may lead to improved Parvoviral product (i.e. higher virus titre) when used to produce recombinant Parvovirus, such as rAAV, as compared to the corresponding wild type. It may lead to a better quality product in terms of having fewer empty virions in comparison to full virions (i.e. virions filled with vector) or to put it another way, a lower (i.e. improved) total/full particle ratio. It may also lead to the accumulation of less residual DNA than a corresponding wild type sequence.

A nucleic acid of the invention may be one which produces a measurable improvement in any such relevant property, for example one of those mentioned above, in comparison to the corresponding wild type sequence. Preferred nucleic acids are those which show an improvement as compared to the wild type in any relevant property of at least about 10%, at least about 25%, at least about 50%, at least about 100%, at least about 200%, at least about 500% or at least about 1000% or more.

The positions in the variant/mutant sequences of the invention set out above are defined with reference to SEQ ID NO: 2 which is the AAV2 Rep78 sequence. A corresponding position in a different Parvoviral Rep sequence, say an AAV5 sequence, may be identified by aligning the two sequences, typically in an optimal way. That would allow the corresponding positions in a wild type sequence (other than that of SEQ ID NO: 2) to be identified and thus the positions at which mutations (such as substitutions) may be incorporated to derive a nucleic acid of the invention.

The terms “percent identity” or “homology” are used interchangeably herein. For the purpose of this invention, it is defined here that in order to determine the percent identity of two amino acid sequences or two nucleic acid sequences, the sequences are aligned for optimal comparison purposes (e.g., gaps can be introduced in the sequence of a first amino acid or nucleic acid for optimal alignment with a second amino or nucleic acid sequence). The amino acid or nucleotide residues at corresponding amino acid or nucleotide positions are then compared. When a position in the first sequence is occupied by the same amino acid or nucleotide residue as the corresponding position in the second sequence, then the molecules are identical at that position. The percent identity between the two sequences is a function of the number of identical positions shared by the sequences (i.e., % identity=number of identical positions/total number of positions (i.e. overlapping positions)×100). Preferably, the two sequences are the same length.

A sequence comparison may be carried out over the entire lengths of the two sequences being compared or over fragment of the two sequences. Typically, the comparison will be carried out over the full length of the two sequences being compared. However, sequence identity may be carried out over a region of, for example, twenty, fifty, one hundred or more contiguous amino acid residues (or nucleotide residues).

The skilled person will be aware of the fact that several different computer programs are available to determine the homology between two sequences. For instance, a comparison of sequences and determination of percent identity between two sequences can be accomplished using a mathematical algorithm. In a preferred embodiment, the percent identity between two amino acid or nucleic acid sequences is determined using the Needleman and Wunsch (J. Mol. Biol. (48): 444-453 (1970)) algorithm which has been incorporated into the GAP program in the Accelrys GCG software package, using either a Blosum 62 matrix or a PAM250 matrix, and a gap weight of 16, 14, 12, 10, 8, 6, or 4 and a length weight of 1, 2, 3, 4, 5, or 6. The skilled person will appreciate that all these different parameters will yield slightly different results but that the overall percentage identity of two sequences is not significantly altered when using different algorithms.

The protein sequences or nucleotide sequences referred to herein may further be used as a “query sequence” to perform a search against public databases to, for example, identify other family members or related sequences. Such searches can be performed using the BLASTN and BLASTP programs (version 2.0) of Altschul, et al. (1990) J. Mol. Biol. 215:403-10. BLAST protein searches can be performed with the BLASTP program, score=50, wordlength=3 to obtain amino acid sequences homologous to protein molecules of the invention. To obtain gapped alignments for comparison purposes, Gapped BLAST can be utilized as described in Altschul et al., (1997) Nucleic Acids Res. 25(17): 3389-3402. When utilizing BLAST and Gapped BLAST programs, the default parameters of the respective programs (e.g., BLASTP and BLASTN) can be used. See the homepage of the National Center for Biotechnology Information.

Nucleotide sequences encoding parvoviral Rep proteins of the invention may also be defined by their capability to hybridise with the nucleotide sequence of SEQ ID NO.1, respectively, under moderate, or preferably under stringent hybridisation conditions. Stringent hybridisation conditions are herein defined as conditions that allow a nucleic acid sequence of at least about 25, preferably about 50 nucleotides, 75 or 100 and most preferably of about 200 or more nucleotides, to hybridise at a temperature of about 65° C. in a solution comprising about 1 M salt, preferably 6×SSC or any other solution having a comparable ionic strength, and washing at 65° C. in a solution comprising about 0.1 M salt, or less, preferably 0.2×SSC or any other solution having a comparable ionic strength. Preferably, the hybridisation is performed overnight, i.e. at least for 10 hours and preferably washing is performed for at least one hour with at least two changes of the washing solution. These conditions will usually allow the specific hybridisation of sequences having about 90% or more sequence identity.

Moderate conditions are herein defined as conditions that allow a nucleic acid sequences of at least 50 nucleotides, preferably of about 200 or more nucleotides, to hybridise at a temperature of about 45° C. in a solution comprising about 1 M salt, preferably 6×SSC or any other solution having a comparable ionic strength, and washing at room temperature in a solution comprising about 1 M salt, preferably 6×SSC or any other solution having a comparable ionic strength. Preferably, the hybridisation is performed overnight, i.e. at least for 10 hours, and preferably washing is performed for at least one hour with at least two changes of the washing solution. These conditions will usually allow the specific hybridisation of sequences having up to 50% sequence identity. The person skilled in the art will be able to modify these hybridisation conditions in order to specifically identify sequences varying in identity between 50% and 90%.

A nucleic acid as described herein may encode a parvoviral Rep protein which is an adeno-associated virus (AAV) Rep protein. A nucleic acid of the invention may encode a Rep78, a Rep68, a Rep 52 or a Rep 40 protein. A nucleic acid of the invention may be based on an AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8 or AAV9 or any other AAV serotype.

More specifically, a nucleic acid of the invention may comprise a nucleotide sequence as set out in any one of SEQ ID NOs: 5, 7, 9, 11, 13, 15, 17, 19 or 21;

A nucleic acid of the invention may comprise a nucleotide sequence encoding the Rep protein as set out in any one of SEQ ID NOs: 6, 8, 10, 12, 14, 16, 18, 20, or 22.

A nucleic acid comprising two or more nucleotide sequences which encode Rep a protein, one or more of which nucleic acids is as according to any one of the preceding claims.

The invention also provides a Parvoviral Rep protein encoded by a nucleic acid of the invention as defined above.

A nucleic acid of the invention sequence may comprise one open reading frame comprising nucleotide sequences encoding more than one parvoviral Rep protein, wherein the initiation codon for translation of the parvoviral Rep78 protein is a suboptimal initiation codon. The suboptimal initiation codon preferably is an initiation codon that effects partial exon skipping. Partial exon skipping is herein understood to mean that at least part of the ribosomes do not initiate translation at the suboptimal initiation codon of the Rep78 protein but at an initiation codon further downstream, whereby preferably the initiation codon further downstream is the initiation codon of the Rep52 protein. The suboptimal initiation codon preferably effects partial exon skipping upon expression of the nucleotide sequence in an insect cell. Preferably, the suboptimal initiation codon effects partial exon skipping in an insect cell so as to produce in the insect cell a molar ratio of Rep78 to Rep52 in the range of 1:10 to 10:1, 1:5 to 5:1, or 1:3 to 3:1, preferably at about 20-40 hours post infection, more preferably at about 30-40 hours post infection, using a baculovirus expression. The molar ration of the Rep78 and Rep52 may be determined by means of Western blotting as described in Example 2.1.5, preferably using a monoclonal antibody that recognizes a common epitope of both Rep78 and Rep52, or using the antibody described in Example 2.1.5.

The term “suboptimal initiation codon” herein not only refers to the tri-nucleotide intitiation codon itself but also to its context. Thus, a suboptimal initiation codon may consist of an “optimal” ATG codon in a suboptimal context, e.g. a non-Kozak context. However, more preferred are suboptimal initiation codons wherein the tri-nucleotide intitiation codon itself is suboptimal, i.e. is not ATG. Suboptimal is herein understood to mean that the codon is less efficient in the inititiation of translation in an otherwise identical context as compared to the normal ATG codon. Preferably, the efficiency of suboptimal codon is less than 90, 80, 60, 40 or 20% of the efficiency of the normal ATG codon in an otherwise identical context. Methods for comparing the relative efficiency of inititiation of translation are known per se to the skilled person. Preferred suboptimal initiation codons may be selected from ACG, TTG, CTG, and GTG. More preferred is ACG.

Elimination of possible false translation initiation sites in the mutant Rep protein encoding sequences of the invention, other than the Rep78 and Rep52 translation initiation sites, of other parvoviruses will be well understood by an artisan of skill in the art, as will be the elimination of putative splice sites that may be recognised in insect cells. The various modifications of the wild-type parvoviral sequences for proper expression in insect cells is achieved by application of well-known genetic engineering techniques such as described e.g. in Sambrook and Russell (2001) “Molecular Cloning: A Laboratory Manual (3rd edition), Cold Spring Harbor Laboratory, Cold Spring Harbor Laboratory Press, New York. Various further modifications of Rep protein coding regions are known to the skilled artisan which could increase yield of Rep protein. These modifications are within the scope of the present invention.

A nucleic acid of the invention may be comprised within a nucleic acid construct. That is to say, the invention provides a nucleic acid construct comprising a nucleotide sequence as described above, wherein the nucleotide sequence is operably linked to expression control sequences for expression in a host cell, for example an insect cell.

These expression control sequences will at least include a promoter that is active in insect cells. Techniques known to one skilled in the art for expressing foreign genes in insect host cells can be used to practice the invention. Methodology for molecular engineering and expression of polypeptides in insect cells is described, for example, in Summers and Smith. 1986. A Manual of Methods for Baculovirus Vectors and Insect Culture Procedures, Texas Agricultural Experimental Station Bull. No. 7555, College Station, Tex.; Luckow. 1991. In Prokop et al., Cloning and Expression of Heterologous Genes in Insect Cells with Baculovirus Vectors' Recombinant DNA Technology and Applications, 97-152; King, L. A. and R. D. Possee, 1992, The baculovirus expression system, Chapman and Hall, United Kingdom; O'Reilly, D. R., L. K. Miller, V. A. Luckow, 1992, Baculovirus Expression Vectors: A Laboratory Manual, New York; W. H. Freeman and Richardson, C. D., 1995, Baculovirus Expression Protocols, Methods in Molecular Biology, volume 39; U.S. Pat. No. 4,745,051; US2003148506; and WO 03/074714. A particularly suitable promoter for transcription of the nucleotide sequence of the invention encoding of the parvoviral Rep proteins is e.g. the polyhedron promoter. However, other promoters that are active in insect cells are known in the art, e.g. the p10, p35, IE-1 or ΔIE-1 promoters and further promoters described in the above references.

As used herein, the term “operably linked” refers to a linkage of polynucleotide (or polypeptide) elements in a functional relationship. A nucleic acid is “operably linked” when it is placed into a functional relationship with another nucleic acid sequence. For instance, a transcription regulatory sequence is operably linked to a coding sequence if it affects the transcription of the coding sequence. Operably linked means that the DNA sequences being linked are typically contiguous and, where necessary to join two protein encoding regions, contiguous and in reading frame.

“Expression control sequence” refers to a nucleic acid sequence that regulates the expression of a nucleotide sequence to which it is operably linked. An expression control sequence is “operably linked” to a nucleotide sequence when the expression control sequence controls and regulates the transcription and/or the translation of the nucleotide sequence. Thus, an expression control sequence can include promoters, enhancers, internal ribosome entry sites (IRES), transcription terminators, a start codon in front of a protein-encoding gene, splicing signal for introns, and stop codons. The term “expression control sequence” is intended to include, at a minimum, a sequence whose presence are designed to influence expression, and can also include additional advantageous components. For example, leader sequences and fusion partner sequences are expression control sequences. The term can also include the design of the nucleic acid sequence such that undesirable, potential initiation codons in and out of frame, are removed from the sequence. It can also include the design of the nucleic acid sequence such that undesirable potential splice sites are removed. It includes sequences or polyadenylation sequences (pA) which direct the addition of a polyA tail, i.e., a string of adenine residues at the 3′-end of a mRNA, sequences referred to as polyA sequences. It also can be designed to enhance mRNA stability. Expression control sequences which affect the transcription and translation stability, e.g., promoters, as well as sequences which effect the translation, e.g., Kozak sequences, are known in insect cells. Expression control sequences can be of such nature as to modulate the nucleotide sequence to which it is operably linked such that lower expression levels or higher expression levels are achieved.

In the event that expression of a Rep protein in an insect cell is required, in a nucleic acid construct of the invention, the nucleotide sequence may be operably linked to a polyhedron promoter, for example.

As used herein, the term “promoter” or “transcription regulatory sequence” refers to a nucleic acid fragment that functions to control the transcription of one or more coding sequences, and is located upstream with respect to the direction of transcription of the transcription initiation site of the coding sequence, and is structurally identified by the presence of a binding site for DNA-dependent RNA polymerase, transcription initiation sites and any other DNA sequences, including, but not limited to transcription factor binding sites, repressor and activator protein binding sites, and any other sequences of nucleotides known to one of skill in the art to act directly or indirectly to regulate the amount of transcription from the promoter. A “constitutive” promoter is a promoter that is active in most tissues under most physiological and developmental conditions. An “inducible” promoter is a promoter that is physiologically or developmentally regulated, e.g. by the application of a chemical inducer. A “tissue specific” promoter is only active in specific types of tissues or cells.

A further preferred nucleotide sequence of the invention comprises an expression control sequence that comprising a nine nucleotide sequence as described at page 9, lines 14 to 21 of WO2007/148971 or a nucleotide sequence substantially homologous thereto, upstream of the initiation codon of the nucleotide sequence encoding the parvoviral Rep78 protein. A sequence with substantial identity to the nucleotide sequence of SEQ. ID NO: 7 and that will help increase expression of the parvoviral Rep78 protein is e.g. a sequence which has at least 60%, 70%, 80% or 90% identity to the nine nucleotide sequence disclosed in WO2007/148971.

A nucleic acid construct according to the invention may be any suitable vector, for example an insect cell-compatible vector, preferably a baculoviral vector. Thus, preferably the nucleic acid construct for expression of a parvoviral Rep protein in insect cells is an insect cell-compatible vector. An “insect cell-compatible vector” or “vector” is understood to a nucleic acid molecule capable of productive transformation or transfection of an insect or insect cell. Exemplary biological vectors include plasmids, linear nucleic acid molecules, and recombinant viruses. Any vector can be employed as long as it is insect cell-compatible. The vector may integrate into the insect cells genome but the presence of the vector in the insect cell need not be permanent and transient episomal vectors are also included. The vectors can be introduced by any means known, for example by chemical treatment of the cells, electroporation, or infection. In a preferred embodiment, the vector is a baculovirus, a viral vector, or a plasmid. In a more preferred embodiment, the vector is a baculovirus, i.e. the construct is a baculoviral vector. Baculoviral vectors and methods for their use are described in the above cited references on molecular engineering of insect cells.

The invention further provides an insect cell comprising a nucleic acid or a nucleic acid construct as described herein. A further preferred insect cell may comprise a nucleotide sequence or nucleic acid construct as defined above encoding two or more mutant parvoviral Rep proteins.

Such an insect cell may comprise no more than one type of nucleotide sequence comprising a single open reading frame encoding a parvoviral Rep protein. Preferably the single open reading frame encodes one or more of the parvoviral Rep proteins, more preferably the open reading frame encodes all of the parvoviral Rep proteins, most preferably the open reading frame encodes the full-length Rep 78 protein from which preferably at least both Rep 52 and Rep 78 proteins may be expressed in the insect cell. One or both of said proteins may be encoded by a nucleic acid of the invention.

It is understood herein that the insect cell may comprise more than one copy of the single type of nucleotide sequence, e.g. in a multicopy episomal vector, but that these are multiple copies of essentially one and the same nucleic acid molecule, or at least nucleic acid molecules that encode one and the same Rep amino acid sequence, e.g. nucleic acid molecules that only differ between each other due to the degeneracy of the genetic code. The presence of only a single type of nucleic acid molecule encoding the parvoviral Rep proteins avoids recombination between homologous sequences as may be present in different types of vectors comprising Rep sequences, which may give rise to defective Rep expression constructs that affect (stability of) parvoviral production levels in insect cells. Preferably, in the insect cell, the nucleotide sequence comprising the single open reading frame encoding one or more parvoviral Rep proteins is part of a nucleic acid construct wherein the nucleotide sequence is operably linked to expression control sequences for expression in an insect cell.

Any insect cell which allows for replication of a recombinant parvoviral (rAAV) vector and which can be maintained in culture can be used in accordance with the present invention. For example, the cell line used can be from Spodoptera frugiperda, drosophila cell lines, or mosquito cell lines, e.g., Aedes albopictus derived cell lines. Preferred insect cells or cell lines are cells from the insect species which are susceptible to baculovirus infection, including e.g. Se301, SeIZD2109, SeUCR1, Sf9, Sf900+, Sf21, BTI-TN-5B1-4, MG-1, Tn368, HzAm1, Ha2302, Hz2E5, High Five (Invitrogen, CA, USA) and expresSF+® (U.S. Pat. No. 6,103,526; Protein Sciences Corp., CT, USA).

An insect cell of the invention may further comprise:

-   -   a) a nucleic acid comprising at least one parvoviral inverted         terminal repeat (ITR) nucleotide sequence; and;     -   b) a nucleic acid sequence comprising a nucleotide sequence         encoding parvoviral capsid protein coding sequence operably         linked to expression control sequences for expression in an         insect cell.

In an insect cell of the invention, the nucleic acids in the cell may be comprised within one or more insect cell-compatible vectors, preferably baculoviral vectors.

In an insect cell of the invention, the nucleic acid comprising at least one parvoviral inverted terminal repeat (ITR) nucleotide sequence may further comprise at least one nucleotide sequence encoding a gene product of interest.

The nucleic acid present in the insect cells of the invention, i.e. the sequence comprising at least one parvoviral (AAV) ITR, further comprises at least one nucleotide sequence encoding a gene product of interest, whereby preferably the at least one nucleotide sequence encoding a gene product of interest becomes incorporated into the genome of a recombinant parvoviral (rAAV) vector produced in the insect cell. Preferably, at least one nucleotide sequence encoding a gene product of interest is a sequence suitable for expression in a mammalian cell. Preferably, the nucleotide sequence comprises two parvoviral (AAV) ITR nucleotide sequences and wherein the at least one nucleotide sequence encoding a gene product of interest is located between the two parvoviral (AAV) ITR nucleotide sequences. Preferably, the nucleotide sequence encoding a gene product of interest (for expression in the mammalian cell) will be incorporated into the recombinant parvoviral (rAAV) vector produced in the insect cell if it is located between two regular ITRs, or is located on either side of an ITR engineered with two D regions.

The nucleic acid defined herein above may thus comprise a nucleotide sequence encoding at least one “gene product of interest” for expression in a mammalian cell, located such that it will be incorporated into an recombinant parvoviral (rAAV) vector replicated in the insect cell. Any nucleotide sequence can be incorporated for later expression in a mammalian cell transfected with the recombinant parvoviral (rAAV) vector produced in accordance with the present invention. The nucleotide sequence may e.g. encode a protein it may express an RNAi agent, i.e. an RNA molecule that is capable of RNA interference such as e.g. a shRNA (short hairpinRNA) or an siRNA (short interfering RNA). “siRNA” means a small interfering RNA that is a short-length double-stranded RNA that are not toxic in mammalian cells (Elbashir et al., 2001, Nature 411: 494-98; Caplen et al., 2001, Proc. Natl. Acad. Sci. USA 98: 9742-47). In a preferred embodiment, such a nucleotide sequence may comprise two nucleotide sequences and each encodes one gene product of interest for expression in a mammalian cell. Each of the two nucleotide sequences encoding a product of interest is located such that it will be incorporated into a recombinant parvoviral (rAAV) vector replicated in the insect cell.

The product of interest for expression in a mammalian cell may be a therapeutic gene product. A therapeutic gene product can be a polypeptide, or an RNA molecule (siRNA), or other gene product that, when expressed in a target cell, provides a desired therapeutic effect such as e.g. ablation of an undesired activity, e.g. the ablation of an infected cell, or the complementation of a genetic defect, e.g. causing a deficiency in an enzymatic activity. Examples of therapeutic polypeptide gene products include CFTR, Factor IX, Lipoprotein lipase (LPL, preferably LPL S447X; see WO 01/00220), Apolipoprotein A1, Uridine Diphosphate Glucuronosyltransferase (UGT), Retinitis Pigmentosa GTPase Regulator Interacting Protein (RP-GRIP), and cytokines or interleukins like e.g. IL-10.

Alternatively, or in addition as a second gene product, a nucleic acid may comprise a nucleotide sequence encoding a polypeptide that serves as a marker protein to assess cell transformation and expression. Suitable marker proteins for this purpose are e.g. the fluorescent protein GFP, and the selectable marker genes HSV thymidine kinase (for selection on HAT medium), bacterial hygromycin B phosphotransferase (for selection on hygromycin B), Tn5 aminoglycoside phosphotransferase (for selection on G418), and dihydrofolate reductase (DHFR) (for selection on methotrexate), CD20, the low affinity nerve growth factor gene. Sources for obtaining these marker genes and methods for their use are provided in Sambrook and Russel (2001) “Molecular Cloning: A Laboratory Manual (3^(rd) edition), Cold Spring Harbor Laboratory, Cold Spring Harbor Laboratory Press, New York. Furthermore, a nucleic acid used in the invention may comprise a nucleotide sequence encoding a polypeptide that may serve as a fail-safe mechanism that allows curing of a subject from cells transduced with the recombinant parvoviral (rAAV) vector of the invention, if deemed necessary. Such a nucleotide sequence, often referred to as a suicide gene, encodes a protein that is capable of converting a prodrug into a toxic substance that is capable of killing the transgenic cells in which the protein is expressed. Suitable examples of such suicide genes include e.g. the E. coli cytosine deaminase gene or one of the thymidine kinase genes from Herpes Simplex Virus, Cytomegalovirus and Varicella-Zoster virus, in which case ganciclovir may be used as prodrug to kill the transgenic cells in the subject (see e.g. Clair et al., 1987, Antimicrob. Agents Chemother. 31: 844-849).

In another embodiment one of the gene products of interest can be an AAV protein. In particular, a Rep protein, such as Rep78 or Rep68, or a functional fragment thereof. A nucleotide sequence encoding a Rep78 and/or a Rep68, if present on the genome of a recombinant parvoviral (rAAV) vector of the invention and expressed in a mammalian cell transduced with the vector, allows for integration of the recombinant parvoviral (rAAV) vector into the genome of the transduced mammalian cell. Expression of Rep78 and/or Rep68 in an rAAV-transduced or infected mammalian cell can provide an advantage for certain uses of the recombinant parvoviral (rAAV) vector, by allowing long term or permanent expression of any other gene product of interest introduced in the cell by the vector.

In the recombinant parvoviral (rAAV) vectors of the invention the at least one nucleotide sequence(s) encoding a gene product of interest for expression in a mammalian cell, preferably is/are operably linked to at least one mammalian cell-compatible expression control sequence, e.g., a promoter. Many such promoters are known in the art (see Sambrook and Russel, 2001, supra). Contitutive promoters that are broadly expressed in many cell-types, such as the CMV promoter may be used. However, more preferred will be promoters that are inducible, tissue-specific, cell-type-specific, or cell cycle-specific. For example, for liver-specific expression a promoter may be selected from an al-anti-trypsin promoter, a thyroid hormone-binding globulin promoter, an albumin promoter, LPS (thyroxine-binding globlin) promoter, HCR-ApoCII hybrid promoter, HCR-hAAT hybrid promoter and an apolipoprotein E promoter. Other examples include the E2F promoter for tumor-selective, and, in particular, neurological cell tumor-selective expression (Parr et al., 1997, Nat. Med. 3:1145-9) or the IL-2 promoter for use in mononuclear blood cells (Hagenbaugh et al., 1997, J Exp Med; 185: 2101-10).

In the context of the invention “at least one parvoviral ITR nucleotide sequence” is understood to mean a palindromic sequence, comprising mostly complementary, symmetrically arranged sequences also referred to as “A,” “B,” and “C” regions. The ITR functions as an origin of replication, a site having a “cis” role in replication, i.e., being a recognition site for trans-acting replication proteins such as e.g. Rep 78 (or Rep68) which recognize the palindrome and specific sequences internal to the palindrome. One exception to the symmetry of the ITR sequence is the “D” region of the ITR. It is unique (not having a complement within one ITR). Nicking of single-stranded DNA occurs at the junction between the A and D regions. It is the region where new DNA synthesis initiates. The D region normally sits to one side of the palindrome and provides directionality to the nucleic acid replication step. An parvovirus replicating in a mammalian cell typically has two ITR sequences. It is, however, possible to engineer an ITR so that binding sites are on both strands of the A regions and D regions are located symmetrically, one on each side of the palindrome. On a double-stranded circular DNA template (e.g., a plasmid), the Rep78- or Rep68-assisted nucleic acid replication then proceeds in both directions and a single ITR suffices for parvoviral replication of a circular vector. Thus, one ITR nucleotide sequence can be used in the context of the present invention. Preferably, however, two or another even number of regular ITRs may be used. Most preferably, two ITR sequences are used. A preferred parvoviral ITR is an AAV ITR. For safety reasons it may be desirable to construct a recombinant parvoviral (rAAV) vector that is unable to further propagate after initial introduction into a cell. Such a safety mechanism for limiting undesirable vector propagation in a recipient may be provided by using rAAV with a chimeric ITR as described in US2003148506.

The number of nucleic acid constructs employed in the insect cell for the production of the recombinant parvoviral (rAAV) vector is not limiting in the invention. For example, one, two, three, four, five, or more separate constructs can be employed to produce rAAV in insect cells in accordance with the methods of the present invention. If five constructs are employed, one construct encodes AAV VP 1, another construct encodes AAV VP2, yet another construct encodes AAV VP3, still yet another construct encodes the Rep protein as defined above and a final construct comprises at least one AAV ITR. If fewer than five constructs are used, the constructs can comprise various combinations of the at least one AAV ITR and the VP1, VP2, VP3, and the Rep protein coding sequences. Preferably, two constructs or three constructs are used, with two constructs being more preferred as described above. If two constructs are used, preferably the insect cell comprises: (a) a nucleic acid construct for expression of the Rep proteins as defined above, which construct further comprises nucleotide sequences as defined in (b) above (comprising parvoviral Cap protein coding sequences operably linked to at least one expression control sequence for expression in an insect cell; see also below); and (c) a nucleic acid construct comprising the nucleotide sequence as defined in (a) above (comprising at least one parvoviral/AAV ITR nucleotide sequence). If three constructs are used, preferably the same configuration as used for two constructs is used except that separate constructs are used for expression of the capsid proteins and for expression of the Rep proteins. The sequences on each construct can be in any order relative to each other. For example, if one construct comprises ITRs and an ORF comprising nucleotide sequences encoding VP capsid proteins, the VP ORF can be located on the construct such that, upon replication of the DNA between ITR sequences, the VP ORF is replicated or not replicated. For another example, the Rep coding sequences and/or the ORF comprising nucleotide sequences encoding VP capsid proteins can be in any order on a construct. In is understood that also the further nucleic acid construct(s) preferably are an insect cell-compatible vectors, preferably a baculoviral vectors as described above. Alternatively, in the insect cell of the invention, one or more of the nucleotide sequences may be stably integrated in the genome of the insect cell. One of ordinary skill in the art knows how to stably introduce a nucleotide sequence into the insect genome and how to identify a cell having such a nucleotide sequence in the genome. The incorporation into the genome may be aided by, for example, the use of a vector comprising nucleotide sequences highly homologous to regions of the insect genome. The use of specific sequences, such as transposons, is another way to introduce a nucleotide sequence into a genome.

In the invention, the nucleotide sequence comprising parvoviral capsid (Cap) protein coding sequences is herein understood to comprises sequences encoding each of the three parvoviral capsid proteins, VP1, -2 and -3. The nucleotide sequence comprising the capsid protein coding sequences may be present in various forms. E.g. separate coding sequences for each of the capsid proteins VP1, -2 and -3 may used, whereby each coding sequence is operably linked to expression control sequences for expression in an insect cell. More preferably, however, such a nucleotide sequence comprises a single open reading frame encoding all three of the animal parvoviral (AAV) VP1, VP2, and VP3 capsid proteins, wherein the initiation codon for translation of the VP1 capsid protein is a suboptimal initiation codon that is not ATG as e.g. described by Urabe et al. (2002, supra). A suboptimal initiation codon for the VP1 capsid protein may be as defined above for the Rep78 protein. More preferred suboptimal initiation codons for the VP1 capsid protein may be selected from ACG, TTG, CTG and GTG, of which CTG and GTG are most preferred. A preferred nucleotide sequence for the expression of the capsid proteins further comprises an expression control sequence comprising a nine nucleotide sequence as disclosed at page 9, lines 14 to 21 of WO2007/148971 or a nucleotide sequence substantially homologous thereto, upstream of the initiation codon of the nucleotide sequence encoding the VP1 capsid protein. A sequence with substantial identity to the nucleotide sequence of disclosed in WO2007/148971 and that will help increase expression of VP1 is e.g. a sequence which has at least 60%, 70%, 80% or 90% identity to the said nine nucleotide. A further preferred third nucleotide sequence for expression of the capsid proteins further preferably comprises at least one modification of the nucleotide sequence encoding the VP1 capsid protein selected from among a C at nucleotide position 12, an A at nucleotide position 21, and a C at nucleotide position 24 (with reference to position 1 being the first nucleotide of the translation initiation codon; see the VP capsid sequence as disclosed in WO2007/148971. Elimination of possible false initiation codons for translation of VP1 of other serotypes will be well understood by an artisan of skill in the art, as will be the elimination of putative splice sites that may be recognised in insect cells. Various further modifications of VP coding regions are known to the skilled artisan which could either increase yield of VP and virion or have other desired effects, such as altered tropism or reduce antigenicity of the virion. These modifications are within the scope of the present invention. Preferably the nucleotide sequence of the invention encoding the parvoviral capsid proteins is operably linked to expression control sequences for expression in an insect cell, which will at least include a promoter that is active in insect cells. Such control sequences and further techniques and materials (e.g. vectors) for expressing parvoviral capsid proteins in insect host cells are already described above for the Rep proteins.

AAV is able to infect a number of mammalian cells. See, e.g., Tratschin et al. (1985, Mol. Cell Biol. 5:3251-3260) and Grimm et al. (1999, Hum. Gene Ther. 10:2445-2450). However, AAV transduction of human synovial fibroblasts is significantly more efficient than in similar murine cells, Jennings et al., Arthritis Res, 3:1 (2001), and the cellular tropicity of AAV differs among serotypes. See, e.g., Davidson et al. (2000, Proc. Natl. Acad. Sci. USA, 97:3428-3432), who discuss differences among AAV2, AAV4, and AAV5 with respect to mammalian CNS cell tropism and transduction efficiency.

AAV sequences that may be used in the present invention for the production of recombinant AAV vectors in insect cells can be derived from the genome of any AAV serotype. Generally, the AAV serotypes have genomic sequences of significant homology at the amino acid and the nucleic acid levels, provide an identical set of genetic functions, produce virions which are essentially physically and functionally equivalent, and replicate and assemble by practically identical mechanisms. For the genomic sequence of the various AAV serotypes and an overview of the genomic similarities see e.g. GenBank Accession number U89790; GenBank Accession number J01901; GenBank Accession number AF043303; GenBank Accession number AF085716; Chlorini et al. (1997, J. Vir. 71: 6823-33); Srivastava et al. (1983, J. Vir. 45:555-64); Chlorini et al. (1999, J. Vir. 73:1309-1319); Rutledge et al. (1998, J. Vir. 72:309-319); and Wu et al. (2000, J. Vir. 74: 8635-47). AAV serotypes 1, 2, 3, 4 and 5 are preferred source of AAV nucleotide sequences for use in the context of the present invention. Preferably the AAV ITR sequences for use in the context of the present invention are derived from AAV1, AAV2, and/or AAV4. Likewise, the Rep (Rep78 and Rep52) coding sequences are preferably derived from AAV1, AAV2, and/or AAV4. The sequences coding for the VP1, VP2, and VP3 capsid proteins for use in the context of the present invention may however be taken from any of the known 42 serotypes, more preferably from AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8 or AAV9 or newly developed AAV-like particles obtained by e.g. capsid shuffling techniques and AAV capsid libraries.

AAV Rep and ITR sequences are particularly conserved among most serotypes. The Rep78 proteins of various AAV serotypes are e.g. more than 89% identical and the total nucleotide sequence identity at the genome level between AAV2, AAV3A, AAV3B, and AAV6 is around 82% (Bantel-Schaal et al., 1999, J. Virol., 73(2):939-947). Moreover, the Rep sequences and ITRs of many AAV serotypes are known to efficiently cross-complement (i.e., functionally substitute) corresponding sequences from other serotypes in production of AAV particles in mammalian cells. US2003148506 reports that AAV Rep and ITR sequences also efficiently cross-complement other AAV Rep and ITR sequences in insect cells.

The AAV VP proteins are known to determine the cellular tropicity of the AAV virion. The VP protein-encoding sequences are significantly less conserved than Rep proteins and genes among different AAV serotypes. The ability of Rep and ITR sequences to cross-complement corresponding sequences of other serotypes allows for the production of pseudotyped rAAV particles comprising the capsid proteins of a serotype (e.g., AAV3) and the Rep and/or ITR sequences of another AAV serotype (e.g., AAV2). Such pseudotyped rAAV particles are a part of the present invention.

Modified “AAV” sequences also can be used in the context of the present invention, e.g. for the production of rAAV vectors in insect cells. Such modified sequences e.g. include sequences having at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95%, or more nucleotide and/or amino acid sequence identity (e.g., a sequence having about 75-99% nucleotide sequence identity) to an AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8 or AAV9 ITR, Rep, or VP can be used in place of wild-type AAV ITR, Rep, or VP sequences.

Although similar to other AAV serotypes in many respects, AAV5 differs from other human and simian AAV serotypes more than other known human and simian serotypes. In view thereof, the production of rAAV5 can differ from production of other serotypes in insect cells. Where methods of the invention are employed to produce rAAV5, it is preferred that one or more constructs comprising, collectively in the case of more than one construct, a nucleotide sequence comprising an AAV5 ITR, a nucleotide sequence comprises an AAV5 Rep coding sequence (i.e. a nucleotide sequence comprises an AAV5 Rep78). Such ITR and Rep sequences can be modified as desired to obtain efficient production of rAAV5 or pseudotyped rAAV5 vectors in insect cells. E.g., the start codon of the Rep sequences can be modified, VP splice sites can be modified or eliminated, and/or the VP1 start codon and nearby nucleotides can be modified to improve the production of rAAV5 vectors in the insect cell.

In an insect cell of the invention, the Parvovirus may be adeno-associated virus (AAV).

The invention also provides a method for producing a recombinant parvoviral virion in an insect cell, the virion comprising a nucleotide sequence the nucleic acid comprising at least one parvoviral inverted terminal repeat (ITR) nucleotide sequence and, optionally, at least one nucleotide sequence encoding a gene product of interest, which method comprises:

-   -   a) culturing an insect cell as defined herein which comprises at         least one parvoviral inverted terminal repeat (ITR) nucleotide         sequence and, optionally, at least one nucleotide sequence         encoding a gene product of interest under conditions such that a         recombinant parvoviral virion is produced; and,     -   b) recovering the recombinant parvoviral virion.

A “recombinant parvoviral virion or AAV vector” (or “rAAV virion or vector”) herein refers to a vector comprising one or more polynucleotide sequences of interest, genes of interest or “transgenes” that are flanked by parvoviral or AAV inverted terminal repeat sequences (ITRs). Such rAAV vectors can be replicated and packaged into infectious viral particles when present in an insect host cell that is expressing AAV rep and cap gene products (i.e. AAV Rep and Cap proteins). When an rAAV vector is incorporated into a larger nucleic acid construct (e.g. in a chromosome or in another vector such as a plasmid or baculovirus used for cloning or transfection), then the rAAV vector is typically referred to as a “pro-vector” which can be “rescued” by replication and encapsidation in the presence of AAV packaging functions and necessary helper functions.

In another aspect the invention thus relates to a method for producing a recombinant parvoviral (rAAV) virion (comprising a recombinant parvoviral (rAAV) vector as defined above) in an insect cell. Preferably, the method comprises the steps of: (a) culturing an insect cell as defined in herein above under conditions such that recombinant parvoviral (rAAV) vector is produced; and, (b) recovering of the recombinant parvoviral (rAAV) vector. It is understood here that the recombinant parvoviral (rAAV) vector produced in the method preferably is an infectious parvoviral or AAV virion that comprise the recombinant parvoviral (rAAV) vector nucleic acids. Growing conditions for insect cells in culture, and production of heterologous products in insect cells in culture are well-known in the art and described e.g. in the above cited references on molecular engineering of insects cells.

Preferably the method further comprises the step of affinity-purification of the (virions comprising the) recombinant parvoviral (rAAV) vector using an anti-AAV antibody, preferably an immobilised antibody. The anti-AAV antibody preferably is an monoclonal antibody. A particularly suitable antibody is a single chain camelid antibody or a fragment thereof as e.g. obtainable from camels or llamas (see e.g. Muyldermans, 2001, Biotechnol. 74: 277-302). The antibody for affinity-purification of rAAV preferably is an antibody that specifically binds an epitope on a AAV capsid protein, whereby preferably the epitope is an epitope that is present on capsid protein of more than one AAV serotype. E.g. the antibody may be raised or selected on the basis of specific binding to AAV2 capsid but at the same time also it may also specifically bind to AAV1, AAV3 and AAV5 capsids.

In a further aspect the invention relates to a rAAV virion produced in the above described methods of the invention, using the nucleic acid constructs and cells as defined above. Preferably the rAAV virion comprises in its genome at least one nucleotide sequence encoding a gene product of interest, whereby the at least one nucleotide sequence is not a native AAV nucleotide sequence, and whereby in the stoichiometry of the AAV VP1, VP2, and VP3 capsid proteins the amount of VP1: (a) is at least 100, 105, 110, 120, 150, 200 or 400% of the amount of VP2; or (b) is at least 8, 10, 10.5, 11, 12, 15, 20 or 40% of the amount of VP3; or (c) is at least as defined in both (a) and (b). Preferably, the amount of VP1, VP2 and VP3 is determined using an antibody recognising an epitope that is common to each of VP1, VP2 and VP3. Various immunoassays are available in the art that will allow quantify the relative amounts of VP1, VP2 and/or VP3 (see e.g. Using Antibodies, E. Harlow and D. Lane, 1999, Cold Spring Harbor Laboratory Press, New York). An suitable antibody recognising an epitope that is common to each of the three capsid proteins is e.g. the mouse anti-Cap B1 antibody (as is commercially available from Progen, Germany). A preferred rAAV virion according to the invention is a virion comprising in its genome at least one nucleotide sequence encoding a gene product of interest, whereby the at least one nucleotide sequence is not a native AAV nucleotide sequence, and whereby the AAV virion comprises a VP1 capsid protein comprises a leucine or a valine at amino acid position 1. A more preferred AAV virion according to the invention has the ratio's of capsid proteins as defined above and comprises a VP1 capsid protein comprises a leucine or a valine at amino acid position 1.

In this document and in its claims, the verb “to comprise” and its conjugations is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. In addition, reference to an element by the indefinite article “a” or “an” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article “a” or “an” thus usually means “at least one”. The disclosure of each reference set forth herein is incorporated herein by reference in its entirety.

The following Examples illustrate the invention:

EXAMPLES Example 1

1.1 Materials and Methods

1.1.1 Cloning of Constructs

1.1.1.1 Construction of Baculovirus Transfer Vector pVD142

Plasmid pVD142 is constructed by inserting the baculovirus p10 promoter in front of the GFP expression cassette in pVD111. Plasmid pVD111 is constructed in several consecutive steps. First, an EcoRV-SapI linker was ligated into SnaBI linearized pDEST8 plasmid (Invitrogen) which comprises the Gateway destination cassette under control of the polyhedrin promoter resulting in pDEST8-linker plasmid. Then, the BBsIxAvrII Gateway destination fragment was isolated from this plasmid, blunted and cloned in between AAV2 ITR sequences by ligating it into pTRCGW that was digested with KpnIxSphI, blunted and dephosphorylated. Subsequently, the ITR-Gateway destination cassette-ITR fragment was obtained by digesting the plasmid with DraIIIxPciI and after blunting it was ligated into the baculovirus transfer vector pAcDB3. In the last step the CMV-GFP expression cassette was isolated from pFBGFPR using SspIxBstAPI, blunted and cloned into the EcoRV linearized pAcDB3 plasmid comprising the Gateway cassette flanked by ITRs resulting in pVD111. Finally, a p10 promoter fragment was amplified from pFBGFPR using the following primers:

The forward primer (AMT primer #327) sequence contains a XbaI site (underlined)

(SEQ ID NO: 23) 5′-TCCGGACTCTAGAGGACCTTTAATTCAACCCAACAC-3′

The reverse primer (AMT primer #332) sequence contains a XhoI site (underlined)

(SEQ ID NO: 24) 5′-GCCTTCGCTCGAGCTCCTTTGATTGTAAATAAAATG-3′

This fragment was digested with XhoIxXbaI and ligated into the pVD111 plasmid which was linearized with the same enzymes resulting in pVD142. The presence of intact ITRs was checked by sequencing, but were not correct. For this reason pVD142 (lot #2) was constructed.

1.1.1.2 Construction of Baculovirus Transfer Vector pVD142(Lot #2)

The vector pVD111 was digested with XhoI*NotI and the 9517 bp fragment was purified from agarose gel using the QIAquick Gel Extraction Kit (Qiagen). The plasmid pVD142 was digested with XhoI*NotI and the 1038 bp fragment was isolated from agarose gel, purified and ligated into the XhoI*NotI digested vector pVD111. Subsequently, the ligation mix was transformed into chemically competent One Shot CcdB survival cells (Invitrogen) plated onto LB plates containing ampicillin and chloramphenicol and grown overnight at 30° C. After miniprep DNA isolation using the GenElute Plasmid Miniprep kit (Sigma-Aldrich) a restriction analysis with XhoI*NotI, MscI, AhdI and SmaI was performed to check on the presence of the p10 promoter and the viral ITRs. To reselect DNA of clone #1 it was transformed into chemically competent SURE-2 cells (Stratagene) and plated onto LB plates containing ampicillin. Maxiprep DNA of pVD142 (lot #2, clone 1.1) was checked with control digestions using EagI*PstI, MscI and SmaI Furthermore, ITRs were checked by sequencing performed by Seqwright. FIG. 1 shows a schematic representation of pVD142(lot #2).

1.1.1.3 Construction of pVD156

To construct the entry vector pVD156 containing the AAV2 Rep78/ACG sequence a PCR was performed on REP-ACG/PSC (patent application WO2007148971; herein also referred to as pVD88) using the following primers:

The forward primer (AMT primer #321) sequence contains a part of the AttB1 site (underlined):

(SEQ ID NO: 25) 5′-CAAAAAAGCAGGCTCCTGTTAAGACGGCGGGG-3′

The reverse primer (AMT primer #322) sequence contains a part of the AttB2 site (underlined)

(SEQ ID NO: 26) 5′-TACAAGAAAGCTGGGTTTATTGTTCAAAGATGCAGTCAT-3′

The PCR protocol and program are described in attachment 3.1 and 3.2, respectively (A-0181 p 005). The PCR product of 1869 bp was purified from gel and used in a second PCR to add the complete AttB sites on each end of the PCR product. This PCR was performed with the following primers:

The forward primer (AMT primer #323) sequence contains the AttB1 site (underlined):

(SEQ ID NO: 27) 5′-GGGGACAAGTTTGTACAAAAAAGCAGGCTCCTGTTA-3′

The reverse primer (AMT primer #324) sequence contains the AttB2 site (underlined)

(SEQ ID NO: 28) 5′-GGGGACCA CTTTGTACAAGAAAGCTGGGTTTATTG-3′

Subsequently, the 1915 bp PCR product was purified from gel and a BP Clonase reaction was performed with the Gateway BP Clonase II enzyme mix. The pDONR221 plasmid (Invitrogen) was used as the entry vector and the reaction was performed according to the Gateway® Technology with Clonase™ II manual Version A. The BP clonase mixture was transformed into chemically competent TOP10 cells (Invitrogen) and plated onto LB plates containing kanamycine. After miniprep DNA isolation using the GenElute Plasmid Miniprep kit (Sigma-Aldrich) a restriction analysis with NcoI and KpnI was performed on the clones to check on the presence of the AAV2 Rep78/ACG cDNA (A-0181 p 024). The sequence of pVD156 was checked by sequencing. Maxiprep DNA was checked again with restriction analysis using NcoI-KpnI and ApaI-EcoRV. FIG. 2 shows a schematic representation of pVD156.

1.1.1.4 Construction of Baculovirus Transfer Vector pVD143

The baculovirus transfer vector pVD143 contains the pPolH-AAV2 Rep78/ACG and the pCMV-p10-GFP expression cassette between ITRs. This plasmid is constructed according to the Gateway® Technology using pVD142 (lot #2) as the destination vector and pVD156 as the entry clone. The LR reaction was performed as described in the Gateway® Technology with Clonase™ II manual Version A, but incubated o/n instead of 1h. The LR clonase mixture was transformed into one vial of chemically competent TOP10 cells (Invitrogen) and added to 300 ml LB medium containing ampicillin. To preserve the two ITR sequences in pVD143 the culture was incubated o/n at 30° C. and thereafter maxiprep DNA was isolated using the QIAGEN Plasmid maxiprep kit (Qiagen). To check the presence of the AAV2 Rep78/ACG expression cassette a restriction analysis with EagI and PstI was performed on the maxiprep DNA and compared to the restriction pattern of the destination vector pVD142. FIG. 3 shows a schematic representation of pVD143.

1.1.1.5 Generation of Rep Error Prone (Rep-EP) Libraries

To introduce random point mutations into the AAV2 Rep78/ACG sequence an error prone (EP) PCR was performed using the GeneMorph II Random Mutagenesis Kit (Stratagene). First, the AAV2 Rep78/ACG sequence was amplified from plasmid pVD88 using the following primers:

The forward primer (AMT primer #321) sequence contains a part of the AttB1 site (underlined):

(SEQ ID NO: 25) 5′-CAAAAAAGCAGGCTCCTGTTAAGACGGCGGGG-3′

The reverse primer (AMT primer #322) sequence contains a part of the AttB2 site (underlined)

(SEQ ID NO: 26) 5′-TACAAGAAAGCTGGGTTTATTGTTCAAAGATGCAGTCAT-3′

The PCR product of 1869 bp was purified from gel and used in the EP-PCR to introduce the random point mutations. To generate Rep error prone (Rep-EP) libraries with different mutation frequencies the initial amount of target DNA was ranging from 0.1 ng to 250 ng, resulting in the libraries Rep-EP1 to Rep-EP5 (Table 1). Five different EP-PCRs were performed with the AMT primerset #321/#322. Subsequently, the Rep-EP PCR products were purified from gel and to add the complete AttB sites a PCR was performed on 100 ng of each Rep-EP library with the following primers:

The forward primer (AMT primer #323) sequence contains the AttB1 site (underlined):

(SEQ ID NO: 27) 5′-GGGGACAAGTTTGTACAAAAAAGCAGGCTCCTGTTA-3′

The reverse primer (AMT primer #324) sequence contains the AttB2 site (underlined)

(SEQ ID NO: 28) 5′-GGGGACCACTTTGTACAAGAAAGCTGGGTTTATTG-3′

Subsequently, the 1915 bp PCR products were purified from gel and a BP recombination reaction was performed with the Gateway BP Clonase II enzyme mix (Invitrogen). The pDONR221 plasmid (Invitrogen) was used as the entry vector and the reactions were performed according to the Gateway® Technology with Clonase™ II manual Version A, with the exception that the reactions were done o/n instead of 1 h. Thereafter, 1 ul of the BP Clonase reaction mixture was transformed into chemically competent TOP10 cells (Invitrogen) and plated onto LB plates containing kanamycine. After o/n culturing of several different clones of each library miniprep DNA was isolated and checked with restriction analysis using NcoI*KpnI. The mutation frequency of each library was estimated by sequencing of two clones of each library using AMT primer #210:

(SEQ ID NO: 29) 5′-AGGCCCAAACAGCCAGATG-3′

Subsequently, the remaining amount of BP reaction mixture of the Rep-EP1 and 3 was transformed into two vials of chemically competent TOP10 cells (Invitrogen), added to 500 ml LB medium containing kanamycine and grown o/n at 30° C. Maxiprep DNAs were isolated using the QIAGEN Plasmid maxiprep kit (Qiagen), checked by restriction analysis using NcoI*KpnI and are named pDONR221-Rep-EP1 and pDONR221-Rep-EP3, respectively.

The two generated pDONR221-Rep-EP libraries were cloned into the destination vector pVD142 with the LR recombination reaction and according to the Gateway® Technology with Clonase™ II manual Version A. For each library the reactions were performed in triplo and incubated for 2 h. Each LR reaction mixture was transformed into one vial of chemically competent TOP10 cells (Invitrogen) and after that the three transformations were combined. To determine the EP library size 30 μl of each transformed library was plated onto LB plates containing ampicillin and the remaining amount was added to 500 ml LB medium. The cultures were incubated o/n at 30° C. to preserve the two ITR sequences present in the destination plasmid and thereafter maxiprep DNA was isolated using the QIAGEN Plasmid maxiprep kit (Qiagen). To check the performance of the LR reaction a restriction analysis with EagI-PstI was performed on the maxiprep DNA and compared to the restriction pattern of the destination vector pVD142 and pVD143. The three pDONR221-Rep-EP libraries that were cloned to the baculovirus transfer vector pVD142 are named pVD142-Rep-EP1 and pVD142-Rep-EP3.

1.1.1.6 Generation of Baculovirus Rep-EP Libraries

To produce baculovirus Rep-EP libraries (Bac.Rep-EP) Sf9 cells were co-transfected with one of the different pVD142-Rep-EP libraries and the flashBAC viral DNA (Oxford Expression Technologies) according to the FlashBAC one-step baculovirus protein expression User Guide, but with the exception of some small changes. In brief, 1×10⁶ Sf9 cells were seeded in a well of 6-wells plate and incubated at 28° C. for 1h to attach. During the incubation the co-transfection mix was prepared by diluting 20 ng of flashBAC DNA and 2 μg pVD142-Rep-EP1 or -EP3 in 500 μl of SF-900II medium (Invitrogen). The transfection reagent Cellfectin from Invitrogen (5 μl) was diluted separately in 500 μl SF-900II medium, added to the DNA mixture and incubated for 15 min at RT. The attached cells were washed once with SF-900II medium and incubated for 5h with the DNA/Cellfectin mixture. Subsequently, 1 ml of fresh SF900II medium (supplemented with 20% FBS) wash added to the cells and 5 days after transfection the Bac.Rep-EP1 and EP-3 p0 were harvested by centrifugation the culture medium at 1900 g for 15 min. The supernatant containing the baculoviruses was transferred to new tubes and stored at 4° C. in the dark. The amplification of the Bac.Rep-EP libraries to p1 was performed in SF+ cells under serum free conditions. Briefly, the Bac.Rep-EP p0 libraries were diluted 1:100 in shaker flasks containing 50 ml SF+ cells at a density of ˜2.0×10⁶ c/ml and harvested three days p.i. as described above. The baculovirus stocks Bac.VD142 and Bac.VD143 were generated simultaneously and in the same way as the Bac.Rep-EP libraries.

After the first selection round the baculovirus libraries Bac.select-EP3 p1 and Bac.EP-EP3 p1 were made in the same way.

The insert of the different Rep baculovirus libraries was checked by performing a PCR on baculoviral DNA isolated from these stocks using the forward primer (AMT primer #349): 5′-GCGGATCATCACAAGTTTGTAC-3′ (SEQ ID NO: 30)

And the reverse primer (AMT primer #350): 5′-ACCACTTTGTACAAGAAAGCTG-3′ (SEQ ID NO: 31)

Baculovirus stocks with the correct insert should generate a 1935 bp fragment.

1.1.1.7 Generation of the Baculovirus Select-EP-EP3 Clones

The Bac.select-EP-EP3 clones were generated in the same manner as the baculovirus libraries. The ORF/Rep ratios of the Bac.select-EP-EP3 clones 1-20 p1 were determined by Q-PCR analysis using the primer sets pr180/181 and pr209/210.

(SEQ ID NO: 32) Pr180: 5′ CGAACCGATGGCTGGACTATC 3′ (SEQ ID NO: 33) Pr181: 5′ TGCTGCTACAAGATTTGGCAAGT 3′ (SEQ ID NO: 34) Pr209: 5′ CTAAACGGGTACGATCCCCAAT 3′ (SEQ ID NO: 29) Pr210: 5′ AGGCCCAAACAGCCAGATG 3′

Due to the variable ORF/Rep ratios a plaque assay was performed, single plaques were amplified to p1 and the ORF/Rep ratios was determined again. Baculovirus stocks with the best ORF/Rep ratio (around value 1) were used in the rAAV5 productions.

1.1.1.8 First Selection Round

During the first selection round rAAV5 productions were performed using the Rep libraries Bac.Rep-EP1 or Bac.Rep-EP3 and Bac.VD92 p5 in a 1:1 ratio. Productions with Bac.VD142 and Bac.VD143 were taken along as control productions. In brief, the different baculovirus stocks were diluted 1:100 in shaker flasks containing in log-phase growing SF+ cells at a density of ˜2.0×10⁶ c/ml. Three days p.i. the rAAV5 productions were harvested by adding 10× lysis buffer and after a 1 h incubation a benzonase treatment was performed at 37° C. Crude lysates were clarified by 1900 g centrifugation and the virus titers were determined using a Q-PCR method with the CMV promoter as target.

1.1.1.9 Second Selection Round

During the second selection round rAAV5 productions were performed using the selected Rep-EP3 library (Bac.selectEP3 p1) or the selected Rep-EP3 library that was subjected to a new mutation round (Bac.EP-EP3 p1) and Bac.VD92 p5 in a 1:1 ratio. Productions with Bac.VD142 and Bac.VD143 were taken along as control productions. Productions were performed as in the first selection round and repeated twice. The rAAV5 virus titers were determined using a Q-PCR method with the CMV promoter as target.

1.1.1.10 Purification of rAAV5 Particles

Crude lysates from the rAAV5 productions with Bac.Rep-EP3 p1 or Bac.EP-EP3 p1 were clarified by 1900 g centrifugation and subsequent filtration using a 0.45 μm Millipak 20 (Millipore) filter. Further purification of the different rAAV5 particles was performed by affinity chromatography AVB sepharose column (GE). The purified rAAV5 batches were stored at −20° C. Viral titers of crude lysates and affinity eluates were determined using a Q-PCR method with the CMV promoter as target.

1.1.1.11 Amplification and Cloning of Selected Rep Libraries

Viral DNA was isolated from the purified rAAV5 samples. In brief, 1/50 volume of DNAse I (Roche) was added to the purified rAAV5 sample and incubated for 20 min at 37° C. To optimize the reaction conditions for proteinase K treatment the end concentrations in the sample were next changed to 10 mM Tris-HCl (pH 8.0), 100 mM NaCl, 10 mM EDTA and 0.5% SDS. Proteinase K (Roche) was added to a final concentration of 2 mg/ml and the proteinase K treatment was performed for 1 h at 37° C. Subsequently, 0.92 volume of RNA lysis buffer (Promega) and poly(A) to a final concentration of 24 ng/ml was added. To bind the viral DNA 1/24 volume of MagneSil BLUE (Promega) was added and the sample was placed on a shaker for 5 min at RT. MagneSil beads were pelleted by 2800 g centrifugation for 5 min at RT, washed once with RNA lysis buffer and two times with 80% ethanol. The MagneSil beads were then transferred to an eppendorf tube and washed twice with 80% ethanol. After transferring to the eppendorf tubes the MagneSil beads were not pelleted by centrifugation, but separated by using the magnetic separation device for eppendorf tubes (Chemagen). The MagneSil beads were incubated at 65° C. until all ethanol was evaporated. Viral DNA was first eluted in 200 μl MQ by incubating for 5 min at 65° C. followed by thoroughly vortexing of the beads and then the supernatant was transferred to a new eppendorf tube. The second elution in 200 μl MQ was performed o/n at 4° C. The two eluates were combined and used in a PCR reaction to amplify and clone the selected Rep library.

To amplify the selected Rep-EP3 library a PCR using AMT primerset #321/#322 was performed on different amounts (2.5, 10 or 250 of isolated viral DNA. The amplified fragments of ˜1869 bp were purified from gel and 10 ng was used in the EP-PCR with AMT primerset #323/#324 to introduce new mutations. Subsequently, the ˜1915 bp PCR products were purified from gel and cloned to pDONR221 as described in section 1.1.1.5, resulting in the pDONR221-EP-EP3 library. The pDONR221-select-EP3 library contains only the Rep-EP3 sequences that were selected in the first round and that were not subjected to a new mutation round. This library was made by performing a PCR on different amounts (2.5 or 10 μl) of isolated viral DNA using the AMT primerset #323/#324 and cloning the amplified products to pDONR221 as described above. Maxiprep DNA isolates from the different libraries were checked with restriction analysis using PstI. The mutation frequency was estimated by sequencing six clones of each library. This sequencing was performed using AMT primer #210. The pDONR221-select-EP3 and pDONR221-EP-EP3 libraries were cloned into the destination vector pVD142 (lot #2) as described in section 1.1.1.5 and are named pVD142-selectEP3 and pVD142-EP-EP3, respectively. To check the performance of the LR reaction a restriction analysis with EagI-PstI was performed on the maxiprep DNA isolates and compared to the restriction pattern of the destination vector pVD142 (lot #2) and pVD143. Recombinant baculovirus stocks comprising these libraries were generated as described in section 1.1.1.6 and are named Bac.select-EP3 and Bac.EP-EP3, respectively.

After the second selection round viral DNA was isolated from the purified rAAV5 sample that was produced with Bac.EP-EP3 p1. The viral DNA isolation, amplification and cloning of the selected EP-EP3 library was performed as described above. This results in the new library named pDONR221-selectEP-EP3. From this library 20 clones were randomly picked and checked with restriction analysis using BstXI. The pDONR221-select-EP-EP3 clones 1-20 were cloned into the destination vector pVD142 (lot #2) as described in section 1.1.1.5 and are named pVD142-select-EP-EP3 clones 1-20. The number of mutations in each clone and the overall mutation frequency was determined by sequence analysis. Subsequently, a baculovirus stock of each clone was generated as described in section 1.1.1.6 and were named Bac.select-EP-EP3 clone 1-20.

1.1.1.12 Productions with Bac.Select-EP-EP3 Clones 1-20

To test the Bac.select-EP-EP3 clones 1-20 in their ability to produce rAAV5 30 ml productions were performed. The Bac.select-EP-EP3 was added in 5:1:1 ratio compared to Bac.VD92 and Bac.VD43. The productions with Bac.VD143 or Bac.VD142 in a 5:1:1 ratio with Bac.VD92 and Bac.VD43 were used again as positive and negative controls, respectively. Finally, virus titers were determined using a Q-PCR method with the CMV promoter as target. Productions with the plaque purified clones were performed in the same way.

1.2 Results

1.2.1 Generation of Rep Error Prone (Rep-EP) Libraries

Five Rep-EP libraries were generated by performing an error prone PCR (EP-PCR) on the 1869 bp fragment that comprises the AAV2 Rep78/ACG expression cassette. By changing the amount of initial target DNA in the different EP-PCRs the number of introduced mutations will alter. After cloning the Rep-EP libraries into the Gateway entry vector pDONR221 the mutation frequencies were determined by partly sequencing of two clones of each library. The estimated amount of mutations per kbp in each library is shown in Table 3. As expected, the library made out of a low initial target DNA has a high mutation frequency and the one made out of a high initial target DNA has a low mutation frequency. The sizes of the five libraries ranged from ˜0.7-1.3×10⁴ clones and were estimated by counting the amount of bacterial colonies that were formed after plating a small percentage of the transformed cells, while the rest of the library was grown in a shaker flask.

TABLE 3 Mutation frequency in the five Rep-EP libraries. Two clones of each Rep-EP library were sequenced using the Rep specific AMT primer #210 and the number of mutations was determined by sequence analysis. The mutation frequency for each library was estimated and is represented as mutations/kbp. Rep library Amount of target DNA Mutations/kbp EP1  0.1 ng ~9-13 EP2  1.0 ng ~7-11 EP3   10 ng ~3-5  EP4   50 ng ~3-6  EP5  250 ng ~0-1 

As the appropriate mutation frequency for the Rep directed evolution has not been established two different Rep-EP libraries were used in the first selection round. The Rep-EP1 and EP3 libraries were cloned to the baculovirus transfer plasmid pVD142(lot #2) using the LR recombination reaction. This results in the libraries pVD142-Rep-EP1 and 3 which were checked again with restriction analysis as shown in FIGS. 4A, 4B, and 4C. The obtained restriction fragments had the expected sizes and were identical to the restriction pattern of pVD143, which contains the non-mutated AAV2 Rep78/ACG expression cassette. The transfer plasmid pVD142 was used as the negative control and was shown to have a different restriction pattern.

1.2.2 First Selection Round

Before starting the selection procedure the baculovirus libraries used were checked by performing a PCR on baculoviral DNA isolated from these stocks. This PCR specifically amplifies the DNA that is present between the two Att recombination sites, the part where the Rep-EP library is located. The PCR on viral DNA from Bac.VD143, Bac.Rep-EP1 and 3 amplified a DNA fragment from the expected size demonstrating that the baculoviruses contain the Rep libraries (FIG. 5). During the first selection round rAAV5 productions were performed using the Rep libraries Bac.Rep-EP1 or 3 p1 and Bac.VD92 p5 in a 1:1 ratio. Productions with Bac.VD142 p1 or Bac.VD143 p1 in a 1:1 ratio with Bac.VD92 p5 were taken along as a negative and positive control production, respectively. Three days p.i. the productions were harvested and the rAAV5 virus titers were determined in crude lysate using the CMV Q-PCR method. The virus titers of the different rAAV5 productions in two independent experiments are shown in Table 4. In both experiments the production with Bac.VD143 gave comparable virus titers. The production with Bac.Rep-EP1 gave a similar virus titer as the negative control production with Bac.VD142. Thus, this is background level. The production with Bac.Rep-EP3 resulted twice in a very low virus titer. However, this virus titer is slightly above background level and indicates that there is probably specific packaging of ssDNA encoding Rep-EP3 sequences. Therefore only the selected Rep-EP3 library was isolated, amplified and re-cloned to the entry vector.

TABLE 4 Virus titers of rAAV5 productions after first selection round. Virus titers of the rAAV5 productions performed in two independent experiments determined with Q-CPR analysis. N.a., not applicable Virus titer (gc/ml) Baculovirus Exp #1 Exp #2 Bac.VD142 n. a. 1.7E+07 Bac.VD143 1.3E+09 1.7E+09 Bac.Rep-EP1 8.5E+07 1.9E+07 Bac.Rep-EP3 8.7E+07 9.7E+07 1.2.3 Amplification and Cloning of Selected Rep-EP3 Library

The rAAV5 particles that were produced during the first selection round with the Rep-EP3 library were purified using affinity chromatography and the viral DNA, presumably containing the selected Rep-EP3 library, was isolated. Subsequently, this selected Rep-EP3 library was amplified by PCR and different amounts of initial target DNA (FIG. 6B). After performing an additional PCR on selected Rep-EP3 library using primerset #323/324 the correct products (˜1915 bp) were purified and cloned into the entry vector pDONR221, resulting in the new libraries pDONR221-select-EP3(2.5 μl) and pDONR221-select-EP3(10 μl). The selected Rep-EP3 library was also subjected to a new mutation round using the GeneMorph II Random Mutagenesis Kit. The 1869 bp fragments were used as a template in the error prone PCR using #323/324. The obtained fragments were purified and cloned to the entry vector resulting in pDONR221-EP-EP3(2.5 μl) and pDONR221-EP-EP3(10 μl). The mutation frequency of the different libraries was also determined again by partly sequencing of three clones of each library. As shown in Table 5 the average mutation frequency for the pDONR221-select-EP3 library is ˜5.9 mutations/kbp and after a new mutation round the frequency was increased to ˜8.2 mutations/kbp.

TABLE 5 Mutation frequency in the select-EP3 libraries. Three clones of each select-EP or EP-EP3 library were sequenced using the Rep specific AMT primer #210 and the number of mutations was determined by sequence analysis. The mutation frequency for each library was estimated and is represented as mutations/kbp. Average Rep library Mutations/kbp Mutations/kbp pDONR221-select-EP3(2.5 μl) ~4.8 ~5.9 pDONR221-select-EP3(10 μl) ~7.0 pDONR221-EP-EP3(2.5 μl) ~4.6 ~8.2 pDONR221-EP-EP3(10 μl) ~11.7

Maxiprep DNA of the two pDONR221-select-EP3 libraries was mixed in an equal ratio and cloned to the baculovirus transfer plasmid pVD142 using the LR recombination reaction, resulting in the library pVD142-select-EP3. The pVD142-EP-EP3 library was generated in the same way. The maxiprep DNA isolates from these two libraries were checked with restriction analysis as shown in FIG. 6C. The obtained restriction fragments had the expected sizes and were identical to the restriction pattern of pVD143. The transfer plasmid pVD142 was used as the negative control and was shown to have a different restriction pattern.

1.2.4 Second Selection Round

Before starting the second selection round the new baculovirus libraries Bac.select-EP3 and Bac.EP-EP3 were generated by recombination of the plasmids libraries with the baculoviral flashBAC DNA and amplified to p1. The control baculoviruses Bac.VD142, Bac.VD143 and Bac.Rep-EP3 were made at the same moment and also amplified to p1. The new baculovirus libraries and control baculoviruses were also checked by PCR analysis. Bac.VD143 and the three Rep baculovirus libraries all revealed the presence of the correct fragment (FIG. 7). During the second selection round 400 ml rAAV5 productions were performed using the baculovirus libraries and Bac.VD92 p5 in a 1:1 ratio and three days p.i. the productions were harvested virus titers were determined in crude lysates using the CMV Q-PCR method. The control productions were performed in 25 ml volumes. The virus titers of the different rAAV5 productions are shown in Table 6.

The control productions with Bac.VD143 and Bac.VD142 gave virus titers of 2.3×10⁹ and 7.4×10⁴ gc/ml, respectively. The production with the selected Rep-EP3 library (Bac.select-EP3) was slightly higher than the production with the Rep-EP3 library used in the first selection round (Bac.Rep-EP3), but both were still very low. Remarkable, the production with Bac.EP-EP3 resulted in 3-fold higher virus titer as compared to Bac.VD143, which could indicate that this library contains more improved Rep proteins than the Bac.select-EP3 library.

TABLE 6 Virus titers of rAAV5 productions after second selection round. Virus titers of the rAAV5 productions were determined with Q-CPR analysis. Baculovirus Virus titer (gc/ml) Bac.VD142 7.4E+04 Bac.VD143 2.3E+09 Bac.Rep-EP3 2.7E+07 Bac.select-EP3 5.7E+07 Bac.EP-EP5 7.6E+09 1.2.5 Cloning of Selected Rep-EP-EP3 Library and Sequence Analysis of 20 Clones

The rAAV5 particles that were produced during the second selection round of the Rep-EP-EP3 library (Table 6) were purified using affinity chromatography and the viral DNA (i.e. the selected Rep-EP-EP3 library) was isolated. Subsequently, this selected Rep-EP-EP3 library was amplified by PCR using primerset #323/324 (FIG. 8) and different amounts of initial target DNA. The ˜1915 bp product obtained with 5 μl initial target DNA was purified and cloned into the entry vector pDONR221, resulting in the new library pDONR221-select-EP-EP3. From this new library 20 clones were randomly picked and checked by restriction analysis. Except for clone 6, the restriction analysis on the different clones and the pDONR221-select-EP-EP3 library revealed the same restriction fragments as the positive control pVD156. Thereafter, the 20 clones were transferred to the plasmid pVD142 using the LR recombination reaction, resulting in pVD142-select-EP-EP3 clones 1-20. Miniprep DNA isolates of these 20 clones were checked with restriction analysis using MscI. The obtained restriction fragments had the expected sizes and were comparable to the restriction pattern of pVD143. The destination plasmid pVD142 was used as the negative control and was shown to have a different restriction pattern.

Before testing all the different clones in rAAV5 productions the complete Rep expression cassette of all clones was sequenced by Baseclear. The mutation frequency is ranging from 2.1-6.4 mutations per kbp and the average frequency is 4.1 mutations per kbp (Table 7). Most mutations were missense mutations (65%) which result in aminoacids changes while the other 19% and 16% were silent and non-sense mutations, respectively. A deletion of 1 or 185 bp was also found in clones 4, 6 and 11.

TABLE 7 Mutation frequency and type of mutations determined in the select-EP-EP3 clones 1-20. Sequence analysis revealed that the average mutation frequency is 4.1 mutations/kbp and 65% of the mutations are missense. Clones 4, 6 and 11 have a 1 bp or 185 bp deletion. deletion Clone # mut # mut/kbp missense silent nonsense (bp) 1 6 3.2 4 1 1 0 2 5 2.7 4 1 0 0 3 6 3.2 3 2 1 0 4 9 4.8 6 1 2 1 5 11 5.9 8 2 1 0 6 6 3.2 5 1 0 185 7 10 5.4 5 3 2 0 8 11 5.9 7 2 2 0 9 12 6.4 7 4 1 0 10 4 2.1 3 1 0 0 11 9 4.8 8 1 0 1 12 8 4.3 4 3 1 0 13 8 4.3 5 1 2 0 14 10 5.4 7 2 1 0 15 6 3.2 4 1 1 0 16 5 2.7 3 0 2 0 17 6 3.2 4 0 2 0 18 7 3.8 5 0 2 0 19 5 2.7 2 2 1 0 20 8 4.3 5 1 2 0 average 4.1 65% 19% 16% 1.2.6 Testing of Rep-Select-EP-EP3 Clones 1-20 on rAAV5 Virus Titers

The Bac.select-EP-EP3 clones 1-20 were tested in rAAV5 productions and virus titers were compared to productions using Bac.VD143 or Bac.VD142. As shown in FIG. 9A productions with clones 4, 6, 7, 9 and 15 generated virus titers that were comparable to background level (Bac.VD142). Clones 1 and 3 gave comparable titers as the positive control Bac.VD183 (FIG. 9A, black bar), while clones 8, 12 and 16-18 generated higher virus titers. Productions with all other clones resulted in lower virus titers as the Bac.VD143, but were above background level.

The product quality of these 20 clones was also checked by determining the ORF/Rep ratios and were shown to be very variable between the different clones. Therefore, the most interesting clones were plaque purified, checked on a correct ORF/Rep ratio (around value 1) and used in the experiment depicted in FIG. 9B. Clones 4, 6, 7, 9, 11 and 15 were excluded from this experiment, because these gave very low virus titers in the previous experiment (see FIG. 9A). Unfortunately, from the plaque assay of clone 8 no baculoviruses could be amplified to p1 and was therefore not included in this experiment. As shown in FIG. 9B the virus titers in the control production is ˜3×10¹⁰ gc/ml and the productions with clones 1, 3 and 14 gave virus titers of 6-7×10¹⁰ gc/ml, while the productions with clones 2, 5 and 10 were lower than the control productions. Productions with clones 12, 13 and 16-20 resulted in virus titers of 1-2×10¹¹ gc/ml, which is 3-5 fold higher as compared to the control productions.

In conclusion, of 20 clones that were randomly picked from the selected Rep-EP-EP3 library 7 clones generated virus titers that were 3-5 folds higher as compared to the control production using the non-mutated AAV2 Rep78/ACG expression cassette.

Example 2

2.1 Materials and methods

2.1.1 Cloning of constructs

2.1.1.1 Construction of pVD210 and pVD215-218 and pVD220

The Rep sequences from REP-ACG/PSC (patent application WO2007148971; herein also referred to as pVD88), pVD142-selectEP-EP3 clone 13, 16-18 and 20 were amplified by PCR using primerset pr460/pr461, digested with PpuMI and XbaI and cloned into the vector pVD88 which was digested with PpuMI*XbaI resulting in the constructs pVD210, pVD215-218 and pVD220, respectively. The forward primer pr460 sequence contains the PpuMI restriction site (underlined): 5′-TACGAGATTGTGATTAAGGTCCCCAG-3′ (SEQ ID NO: 35)

The reverse primer pr461 sequence contains the XbaI restriction site (underlined)

(SEQ ID NO: 36) 5′-CATCACTCTAGACTTACTTGGCTCCACCCTTTTTG-3′

To verify the cloned Rep sequences all constructs were sequenced.

2.1.1.2 Construction of pVD211 and pVD212

The plasmids pVD211 and pVD212 were generated by performing a PCR using primerset pr460/pr462 on pVD142-selectEP-EP3 clone 19 and 20, PCR fragments were digested with PpuMI and SexAI and by cloning these inserts into pVD88 which was digested with PpuMI*SexAI The reverse primer pr462 sequence contains the SexAI restriction site (underlined): 5′-GCTGCTGG CCCACCAGGTAG-3′ (SEQ ID NO: 37)

2.1.1.3 Construction of pVD214

To construct pVD214 the Rep sequence was amplified from pVD142-selectEP-EP3 clone 12 (described in example 1) using primerset pr460/pr463. Plasmid pVD88 digested with PpuMI*XbaI was used as the vector. The reverse primer pr463 sequence contains the XbaI restriction site (underlined): 5′-CATCACTCTAGAATCACT CTAAACAGTCTTTCTGTC-3′ (SEQ ID NO: 38)

2.1.1.3 Construction of pVD228

The Rep68/ACG sequence that is present in pVD228 was generated using primerset pr460/pr487 and pVD88 as template. The PCR fragment was digested with PpuMI and XbaI and cloned in pVD88 digested with the same enzymes resulting in pVD228. Primer pr487 consists of three parts, i.e. an additional sequence which contains an XbaI restriction site (underlined), the 25 bp unique sequence for Rep68 (bold), and the sequence which is homologous with Rep78 (italic): 5′-CATCACTCTAGATTATCAG AGAGAGTGTCCTCGAGCCAATCTGTCTGC GTAGTTGATCG-3′ (SEQ ID NO: 39)

2.1.2 Generation of Recombinant Rep Baculoviruses

Recombinant baculoviruses were generated by co-transfecting Sf9 with one of the different transfer plasmids (i.e. pVD210-212, pVD214-220 and pVD228) and BacPSC1 viral DNA (Protein Sciences). Five days after transfection, the culture medium was harvested and a plaque assay was performed. After 10 days of incubation, recombinant plaques were amplified to p1 and ORF/Rep ratios were determined with Q-PCR method. Correct clones which have an ORF/Rep around 1 were amplified to p2. The amplification of recombinant baculoviruses (p2, p3 and p4) were performed in expresSF+ cells (Protein Sciences, cat no 1000) under serum free conditions.

2.1.3 rAAV5 Productions

To test the different Rep constructs rAAV5 productions were performed in expresSF+ cells using the baculoviruses Bac.Rep:Bac.VD179:Bac.VD92. The baculovirus stock Bac.VD179 contains the SEAP reporter gene under control of the CMV promoter and is flanked by viral AAV2 ITRs. Bac.VD92 contains the AAV5 capsid gene coding for VP1, VP2 and VP3, under control of the Polh promoter. Each production is performed in duplo, repeated three times and compared to the control production with Bac.VD88. The rAAV5 virus titers were measured in the clarified crude lysate using a CMV-Q-PCR method. To isolate intact rAAV5 particles from the crude lysate batch affinity purifications were performed using the AVB Sepharose HP resin. Finally, the eluate was aliquoted and stored at −20° C.

2.1.4 Transgene Replication Assay

Low-molecular weight DNA was isolated from infected expresSF+ cells during rAAV5 productions according to a modified protocol published by Ziegler et al. (Ziegler, K., T. Bui, R. J. Frisque, A. Grandinetti, and V. R. Nerurkar. 2004. A rapid in vitro polyomavirus DNA replication assay. J. Virol. Methods 122:123-127) and using the GenElute plasmid miniprep kit (Sigma-Aldrich). Briefly, 500 μl cell suspension was centrifuged at 12000 g for 1 min. The cell pellet was resuspended in 200 μl Resuspension Solution. Cells were lysed in 200 μl Lysis Solution and incubated at RT for 5 min. Subsequently, 35 μl Proteinase K solution (20 mg/ml) was added and incubated at 55° C. for 30 min. Samples were neutralized by adding 380 μl Neutralization/Binding Solution and incubated on ice for 5 min. After centrifugation at 12000 g for 10 min supernatants were brought on prepared columns and centrifuged at 12000 g for 1 min. Columns were washed with 750 μl Wash Solution and centrifuged twice at 12000 g for 1 min. DNA was eluted in 50 μl 10 mM Tris-HCl (pH8.0) and 2 μl of each sample was separated on a 1% agarose gel containing ethidium bromide.

2.1.5 Western Blot Analyses of Rep Proteins

To the Rep protein expression derived from different Rep baculovirus constructs during rAAV5 production, cell lysates were taken and subjected to western blot analyses. In brief, 450 μl was taken from a production 24h post infection (p.i.), 50 μl 10× lysis buffer and 8 μl Benzonase (diluted to 2.5 U/μl in PBS; Merck, cat no 1.01697.0001) was added. After mixing, the samples were incubated for 45 min on ice. Lysates were centrifuged at 1900 g and 300 uL of the supernatant was mixed with 100 uL 4× NuPage sample buffer containing 200 mM DTT. The samples were incubated at 95° C. for 5 minutes and stored at −20° C. Proteins were separated on a 4-12% Bis-Tris NuPAGE gel (Invitrogen, cat no NP0323BOX) and the proteins were thereafter blotted on a PVDF membrane. First antibody incubation was done with anti-Rep 303.9 antibody (dilution 1:500; Progen, cat. no. #65169). Polyclonal rabbit anti-mouse IgG-HRP (DAKO, cat no P0260) was used as the secondary antibody in a 1:1000 dilution. After three washes with TBS-T the membrane was incubated with 500 μl Lumi-Light plus substrate solution (Roche, cat no 12015196001) for 1-5 min. Subsequently, the chemiluminescent signal was detected with the Image Quant 400.

2.1.6 Residual Baculovirus DNA Analysis

Residual baculovirus DNA impurities present in the rAAV5 batch affinity purified samples were analyzed using the Q-PCR method. Total DNA was isolated from the rAAV5 particles and analysed using Q-PCR. Bac.VD43 baculovirus DNA was used as a standard line instead. The CMV primerset to quantify the amount of transgene and the different primersets used to determine the amount of residual baculovirus DNA are the following:

CMV Primerset:

(SEQ ID NO: 40) Pr59: 5′ AATGGGCGGTAGGCGTGTA 3′ (SEQ ID NO: 41) Pr60: 5′ AGGCGATCTGACGGTTCACTAA 3′

Baculovirus ORF1629 Primerset (595 bp Downstream of R-ITR):

(SEQ ID NO: 32) Pr180: 5′ CGAACCGATGGCTGGACTATC 3′ (SEQ ID NO: 33) Pr181: 5′ TGCTGCTACAAGATTTGGCAAGT 3′

Right of Baculovirus ORF603 Primerset (249 bp Upstream of L-ITR):

(SEQ ID NO: 42) Pr406: 5′ ACAGCCATTGTAATGAGACGCACAA 3′ (SEQ ID NO: 43) Pr407: 5′ CCTAGCGCCCGATCAGCAACTATAT 3′

Baculovirus HR3 Region Primerset (65 Kbp Downstream of R-ITR):

(SEQ ID NO: 44) Pr340: 5′ ATACAACCGTTGGTTGCACG 3′ (SEQ ID NO: 45) Pr341: 5′ CGGGACACGCCATGTATT 3′

Finally, the transgene/residual DNA ratios measured in the different rAAV5 samples were compared to rAAV5 particles produced with Bac.VD88.

2.1.7 Total Particle Assay

The amount of total rAAV5 particles present in the purified batches was determined SyproRuby staining. In brief, equal amounts of each sample were mixed with 4×LDS sample buffer containing 200 mM DTT and heated for 5 min at 90° C. Total protein was stained using SyproRuby and VP3 bands were quantified with the ImageQuantTl software 1D analysis version 7.0 (GE Healthcare). A rAAV5 control sample with known total particle concentration was taken along on each gel and used to determine to total particle concentration in each sample.

2.1.8 Statistical analysis

All data are represented as means±S.E.M. and the statistical analyses involved the ANOVA single factor test using Excel 2003. Statistical significance was set at p<0.05.

2.2 Results

2.2.1 Rep expression

The Rep protein expression from the different Rep baculovirus constructs (FIGS. 10A and 11A) was determined by western blot analysis on lysates obtained 24h p.i. (FIGS. 10B and 11B). The control construct Bac.VD88 expresses the Rep78 and Rep52 proteins and Bac.VD228 the two shorter Rep proteins Rep68 and Rep40, which lack the C-terminal Zinc-finger domain. The baculoviruses Bac.VD210 and Bac.VD215-218 express shortened Rep78 and Rep52 mutant forms that have a molecular weight of ˜60 kDa and ˜30 kDa and are indicated with Reppy78 and Reppy52 (FIG. 10B), respectively. Bac.VD211 encodes for the full length Rep proteins and the expression was shown to be comparable to Bac.VD88. Remarkably, all constructs except for Bac.VD215 and Bac.VD216 showed a cross reactive band which is migrating somewhat faster than the full length Rep78 or Reppy78. This could be the result of an alternative translation start site, because in the Rep sequence in Bac.VD215 and Bac.VD216 an ATG (M) was mutated to a GTG (V) and this constructs does not show this cross reactive band. Interestingly, Bac.VD216 expresses more Reppy52 as compared to the other constructs. The Rep expression pattern of Bac.VD212 which encodes for the full length Rep is comparable to Bac.VD88, but the expression levels are lower (FIG. 11B). Bac.VD220 expresses Reppy78 and Reppy52 mutant forms that have the same molecular weight as the ones expressed by Bac.VD210 and −215-218 (see FIG. 10B), while the shortened Rep proteins expressed by Bac.VD214 are larger and migrate at the expected sizes of ˜65 kDa and ˜39 kDa.

2.2.2 Transgene Replication

In the BEVS-based rAAV production process the expression of Rep78 is required for replicating the therapeutic gene that is flanked by viral ITRs and has to be packaged into the preformed capsids. The baculoviruses Bac.VD215-218 express the shortened Rep78 proteins which also have 1-3 point mutations in their N-terminal domain. This Rep78-specific part comprises the DNA binding domain and mutations in it could affect the binding to the viral ITRs may be resulting in altered replication and/or packaging of the transgene. Replicative forms of the transgene can be detected relatively easily in insect cells (Urabe, M., T. Nakakura, K. Q. Xin, Y. Obara, H. Mizukami, A. Kume, R. M. Kotin, and K. Ozawa. (2006) J. Virol. 80:1874-1885) and was therefore being monitored during rAAV5 production. Bac.VD179 that is used in the different experiments comprises the CMV-SEAP transgene and is ˜3.1 kbp. To get rid off host cell and baculovirus genomic DNA only low-molecular weight DNA was isolated from cell pellets 1, 2 and 3 days p.i. using a plasmid miniprep kit (Ziegler, K., T. Bui, R. J. Frisque, A. Grandinetti, and V. R. Nerurkar. (2004) J. Virol. Methods 122:123-127). The isolated DNA was separated on agarose gels and visualized using ethidium bromide staining as shown in FIGS. 12A and 12B. One day p.i. the monomeric replicative form of the transgene (RFm) is very well detectable in most productions, except for Bac.VD88, −228 and −218 in which only a very small amount of RFm is present. Also a very faint band of ˜6 kbp, which represents the dimeric replicative form (RFd) of the transgene, is present in some productions. At day 2 p.i. (FIGS. 12A and 12B, middle panel) the amount of RFm increased as compared to day 1 and in the productions in which the full length Rep78 is expressed (i.e. Bac.VD88, −211 and −212) the RFd is more abundant as compared to the productions in which Reppy78 is expressed (i.e. Bac.VD210 and Bac.VD214-218). The pattern of the replicated DNA at day 3 p.i. is comparable to that at day 2. Remarkably, in the productions with Bac.VD88, Bac.VD211 and Bac.VD212 much more additional bands and smears are present. In Bac.VD228 and −218 only the RFm is present, but hardly detectable as compared to other productions. In conclusion, in the productions in which the full length Rep78 protein is expressed, much more higher order RFs are detectable suggesting that the full length protein replicates the rAAV genome different than the shortened Reppy78 proteins.

2.2.3 rAAV Productions

To determine whether the Rep mutant constructs can improve the production process rAAV5 productions were performed and virus titers were determined in clarified crude lysate using Q-PCR analysis. The virus titers were calculated as the fold difference to the production with Bac.VD88 and the results are shown in FIG. 13. Expression of Rep68/40 during production (i.e. Bac.VD228) results in a significant lower vector yield. Productions performed with Bac.VD210 and Bac.VD218 increase the vector yield with almost a 2-fold as compared to Bac.VD88. Bac.VD217 expresses the YF mutated Reppy78 and Reppy52 and results in a 2-fold higher vector yield. Bac.VD216 increases the vector yield significantly to almost a 4-fold while Bac.VD215 and Bac.VD220 seem to improve it with a 2.5-fold. Rep expression from Bac.VD214 does not increase the vector yield.

2.2.4 Product Quality

In principal, the most interesting Rep mutant constructs increase the vector yield and at the same moment also improve the product quality by reducing the amount of residual baculovirus DNA and the total/full particle ratio. However, these parameters can only accurately be determined in purified batches and therefore the most interesting productions (i.e. Bac.VD88, −210, −216, −217 and −220) were purified using AVB Sepharorse resin. As shown in FIG. 14 productions with Bac.VD216 and Bac.VD217 improved the total/full ratios with a factor 3.0 and 2.1, respectively. In the rAAV5 batches produced with Bac.VD210 and Bac.VD220 the improvement was less pronounced. To determine whether the presence of unwanted baculovirus DNA is decreased in the rAAV5 batches produced with the Rep mutants three different primer sets that each target a different region in the baculovirus genome were used in Q-PCR performed on DNA isolated from the capsids. As shown in FIG. 15A primer set pr406/407 targets a region 249 bp upstream of the L-ITR which is close to baculovirus ORF603, the so-called left ORF. Primer set pr180/181 targets a region 595 bp downstream of the R-ITR which is located in ORF1629, the so-called right ORF. The third primer set (not depicted in FIG. 15A) pr340/341 targets a region near HR3 which is located 65 kbp downstream from the R-ITR. This target is hypothesized to be a representative for the complete baculovirus genome that is present as residual DNA in the batches. The amount of residual DNA present in the purified rAAV5 batches are represented as transgene to residual DNA ratios and are shown in FIGS. 15B, 15C and 15D.

Productions with the Rep mutant constructs Bac.VD210, −216, −217 and −220 resulted in a significant reduction of the amount of residual baculovirus DNA in the rAAV5 batches. Batches produced with Bac.VD210 and Bac.VD220 were demonstrated to have a 5-fold reduction in the left ORF DNA, a 12- and 11-fold lower amount of right ORF and a 42- and 52-fold reduction of the HR3 region, respectively. Bac.VD217 also significantly reduces the left and right ORF DNA with a 3- and 7-fold and the HR3 region with a 25-fold. The Rep construct that generates the highest vector yields is Bac.VD216 (FIG. 13), but unfortunately only the right ORF and HR3 region are significantly reduced with a 5- and 35-fold and the left ORF DNA is not. 

The invention claimed is:
 1. A nucleic acid construct comprising a nucleic acid comprising a nucleotide sequence encoding an adeno-associated virus (AAV) Rep78 protein, wherein amino acid residues as defined with reference to amino acid residues E57, T97 and C179 of the AAV Rep78 protein of SEQ ID NO: 2 are mutated by substitution of the nucleotide sequence encoding the AAV Rep78 protein, wherein the nucleic acid is operably linked to an expression control sequence for expression in an insect cell.
 2. The nucleic acid construct according to claim 1, further comprising a mutation of amino acid residue corresponding with position 484 or 571 of the AAV Rep78 protein as defined with reference to amino acid residues F484 and C571 of SEQ ID NO:2.
 3. The nucleic acid construct according to claim 1, comprising mutations of amino acid residues at positions 57, 97, 179, 484 and 571 in comparison with a corresponding wild type sequence, said amino acid position being defined with reference to amino acid residues E57, T97, C179, F484 and C571 of SEQ ID NO:2.
 4. The nucleic acid according to claim 1, wherein the AAV Rep78 protein encoded by said nucleic acid has at least 80% sequence similarity to SEQ ID NO:2.
 5. A nucleic acid construct comprising the nucleotide sequence set out in any one of SEQ ID NOs: 9, 11 or
 21. 6. A nucleic acid construct comprising a nucleotide sequence encoding the AAV Rep78 protein as set out in any one of SEQ ID NOs: 10, 12 or
 22. 7. A nucleic acid construct comprising two or more nucleotide sequences which encode an AAV Rep78 protein, one or more of which is as according to claim
 1. 8. An AAV Rep78 protein encoded by a nucleic acid as defined in claim
 1. 9. The nucleic acid construct according to claim 1, wherein the nucleotide sequence is operably linked to a polyhedron promoter.
 10. The nucleic acid construct according to claim 1, wherein the construct is an insect cell-compatible vector.
 11. The nucleic acid construct according to claim 10, wherein the insect-compatible vector is a baculoviral vector.
 12. An isolated insect cell comprising a nucleic acid construct according to claim
 1. 13. The isolated insect cell according to claim 12, wherein the insect cell further comprises: (a) a nucleic acid comprising at least one Parvoviral inverted terminal repeat (ITR) nucleotide sequence; and; (b) a nucleic acid sequence comprising a nucleotide sequence encoding a Parvoviral capsid protein coding sequence operably linked to expression control sequences for expression in an insect cell.
 14. The isolated insect cell according to claim 12, wherein the nucleic acids are comprised within one or more insect cell-compatible vectors.
 15. The isolated insect cell according to claim 14, wherein the one or more insect cell-compatible vectors are baculoviral vectors.
 16. The isolated insect cell according to claim 12, wherein the nucleic acid comprising at least one parvoviral inverted terminal repeat (ITR) nucleotide sequence further comprises at least one nucleotide sequence encoding a gene product of interest.
 17. A method for the production of a recombinant Parvoviral virion in an insect cell, which method comprises: (a) culturing an insect cell according to claim 13 under conditions such that a recombinant parvoviral virion is produced; and, (b) recovering the recombinant parvoviral virion. 